Resolved, That any Corresponding Member who may take up his residence in this city, may become a Resident Member, on notifying the Recording Secretary that such is his wish.
Resolved, That any Corresponding Member who may take up his residence in this city, may become a Resident Member, on notifying the Recording Secretary that such is his wish.
Mr. W. H. Dall was elected a Resident Member, December 4th, 1865.
President in the chair.
Eleven members present.
Donations to the Library: Société de Géographie de Genève; Mémoires et Bulletin, Tomes I-III; From F. Berton.
The following papers were presented.
Note on Octopus punctatus, Gabb.BY W. H. DALL, ACTING DIRECTOR SCI. CORPS W. U. T. EX.A half-decayed specimen of this species, (described by Mr. Gabb, in Proc. Cal. Acad., Ap. 7th, 1862) discovered in some alcoholic miscellanea, recently, afforded the following observations.The buccal plates or mandibles, resemble those ofO. tuberculatus, Blainv. [Woodw. Man. Pl. I.Fig. 2] but are more produced longitudinally. They are black and very brittle.(Fig. 27.)Dental formula, 3·3·3 (Fig. 27, A), or 1/(1×1)·2·1·Rhachisarmed with one central quinquedentate tooth, and two lateral, simple, denticles; the insertion of all is broadly arcuate. Thepleuræare provided each with two simple recurved uncini and one rhomboidal plate with a small recurved hook. The central rhachidian tooth is occasionally irregular. (Fig. 27, L, X). When immature, the dental laminæ are without color, more slender, compressed, and the dentations are less distinct. (Fig. 27, ‛L.) Immature rows, about 15, perfect 60, worn and broken 25, total 100. Mag. 100 diameters. Length of specimen 3 feet. Locality, near San Francisco. From the market.
BY W. H. DALL, ACTING DIRECTOR SCI. CORPS W. U. T. EX.
A half-decayed specimen of this species, (described by Mr. Gabb, in Proc. Cal. Acad., Ap. 7th, 1862) discovered in some alcoholic miscellanea, recently, afforded the following observations.
The buccal plates or mandibles, resemble those ofO. tuberculatus, Blainv. [Woodw. Man. Pl. I.Fig. 2] but are more produced longitudinally. They are black and very brittle.
(Fig. 27.)
(Fig. 27.)
Dental formula, 3·3·3 (Fig. 27, A), or 1/(1×1)·2·1·
Rhachisarmed with one central quinquedentate tooth, and two lateral, simple, denticles; the insertion of all is broadly arcuate. Thepleuræare provided each with two simple recurved uncini and one rhomboidal plate with a small recurved hook. The central rhachidian tooth is occasionally irregular. (Fig. 27, L, X). When immature, the dental laminæ are without color, more slender, compressed, and the dentations are less distinct. (Fig. 27, ‛L.) Immature rows, about 15, perfect 60, worn and broken 25, total 100. Mag. 100 diameters. Length of specimen 3 feet. Locality, near San Francisco. From the market.
Professor Whitney communicated the following abstract of the results obtained by M. Rémond in his geological explorations of Northern Mexico, made in 1863 to 1865, and drawn up from hisnotes and specimens, after reference of the fossils obtained to Mr. Gabb and Dr. Newberry. M. Rémond has gone to Chili to continue his geological investigations, if his health permits; and he expects to write out a more detailed account of his Mexican work, whenever he has an opportunity of doing so. In the mean time, however, it is his desire that this abstract should be drawn up and published, that at least the more important results may be placed as soon as possible in the hands of those interested in the development of the geological structure of those countries which border on the Pacific coast. In presenting this paper, Professor Whitney desired to express his admiration of the courage and endurance with which M. Rémond had prosecuted his investigations in Mexico, where he had to contend with every kind of difficulty and danger, but where, however, he had obtained results of great value, throwing the first rays of light on the age of the formations of a very interesting and economically important mining region—a region which has been often visited, but where, previous to M. Rémond’s examinations, no positive evidence of the geological position of any of the stratified rocks had been obtained, and no clue given to the relations of the metalliferous veins to each other, or to the rocks in which they are inclosed.
Notice of Geological Explorations in Northern Mexico.BY A. RÉMOND.[Compiled from his notes, and prepared for publication, by J. D. Whitney.]1.Preliminary Remarks.The mountainous region comprising the central and western portion of Northern Mexico, belongs to the four States of Durango, Chihuahua, Sinaloa, and Sonora. Considering how celebrated this portion of Mexico has become for its mines and metalliferous veins, and how much has been written about it, it is surprising how little exact information has hitherto been obtained with regard to either its geography or geology. On comparing the principal published maps[21]of the region in question, it will be seen at once how much they differ from each other in their delineations of even its main topographical features, while the details are entirely wanting.The name of the “Sierra Madre” is usually applied to the main range of mountains of this country, or the western border of the plateau which stretches north through the territories of the United States, forming what may be called the great orographical feature of the continent. In Northwestern Mexico this crumpled border of the great plateau comprises an extensive mountainous region, by no means forming a continuous single chain, but rather several central ranges, with associated groups of parallel ridges, all having the same general course, which is approximately north-northwest, and south-southeast. As the breadth of the chain widens as we go towards the north, so, too, that of the valleys increases in that direction, the whole system of mountains and valleys spreading out in something like a fan shape.Going north, the chain appears to sink gradually, although determinations of altitude in Northern Mexico are extremely few in number. It is certain that there is, in about latitude 32°, a depression of the mountain ranges which extends entirely across the continent, and which would enable the traveler to cross from the Atlantic to the Pacific, without necessarily surmounting any elevation greater than four thousand feet.[22]The southeastern range is the highest, and the culminating point is said to be the Cerro de Cuiteco, sixty leagues northeast of Jesus Maria, on the western border of Chihuahua. The approximate altitude of the Cumbre de Basascachic is seven thousand four hundred and twenty-nine feet, and that of Guadalupe y Calvo, seven thousand eight hundred and twenty-five feet. To the north, the ranges east of Sahuaripa are also very high; but they have never been measured. No peaks or ridges, however, in this portion of Mexico attain anything like the elevation of the higher portion of the Sierra Nevada, few if any points exceeding ten thousand feet in altitude.The direction of the sierra is nearly that of a line connecting some of the best mining districts in Mexico, which are situated on or very near the summit of the mountains. These districts are the following, enumerating them in their geographical order from the south towards the north: In Durango, San Antonio de las Ventanas, Guarisamey, and San Dimas, remarkable for their auriferous silver ores, and sixty-two Mexican leagues northeast of Mazatlan; in Chihuahua, Guadalupe y Calvo, and San Pedro de Batopilas, yielding fine specimens of native silver; also, Jesus Maria, in the same State, and the Real del la Cieneguita, Sonora, with silver and gold mines.2.General Geology.The geological structure of the occidental slope of the Sierra Madre, as well as that of the other parts of this great chain, is exceedingly interesting, and, as yet but very little known, notwithstanding the valuable investigations of Humboldt and other eminent men; for, up to the present time, the age of the different formations has never been fixed with any degree of accuracy, from want of materials and of sufficient observations. In 1863, 1864, and 1865, however, I explored quite a number of localities in northwestern Mexico, and was thusenabled to obtain a pretty good general idea of the geology of that region; and, in Sonora, to which my attention was especially devoted, I succeeded in finding fossils in sufficient quantity to allow of the determination of the age of the principal formations of the northern Sierra Madre. By tracing the connection of these rocks with those of Central Mexico, additional light will be thrown on those districts of which, at present, but little is definitely known.The igneous rocks, which occur more abundantly on the Pacific slope, are granites, either fine or very coarse-grained; porphyries, more or less feldspathic; and greenstones, all of which are cut by numerous dykes of extremely varied character. The granites, however, are very poor in veins of the precious metals, while the porphyries are highly metalliferous. In Sinaloa (Candelero) and Durango (San Dimas) we see that the granites underlie the metalliferous porphyries, and that the greenstones, in Sonora, (near Hermosillo and in the vicinity of La Haciendita) penetrate through them.The oldest sedimentary rocks, which I have observed, belong to the Carboniferous series; this is represented in the eastern part of Sonora, by heavy masses of limestone, forming very high and rugged ridges, running a little west of north. The upturned strata are seen, in many places, to rest on granite. Argentiferous veins occur throughout this formation.The next group of sedimentary rocks, in order, is the Triassic; this forms isolated mountain groups in Sonora, and offers an interesting field for investigation. Instead of limestones, it is made up of heavy beds of quartzites and conglomerates, with coal-bearing clay shales; all of these are disturbed and elevated, and rest on greenstones, feldspathic porphyries, or granite. Wherever metamorphosed, the Triassic rocks are auriferous and contain veins of silver ores. The metamorphic slates and limestones of the Altar and Magdalena districts, which include the richest gold placers of Sonora, may possibly be of Triassic age; but the fossils collected are too imperfect to admit of this being determined. There are some reasons for believing those rocks to be rather of Jurassic than of Triassic age, as they differ in lithological characters from both the Triassic and Carboniferous of Northern Mexico, resembling, rather, the Jurassic gold-bearing slates of the Sierra Nevada, in California; besides, they lie outside and to the west of the Sierra Madre. It may also be noticed that the gold which they furnish does not resemble that obtained from the Triassic strata.The Cretaceous period is also represented at the foot of the Sierra Madre, at Arivechi, in Sonora. The strata belonging to this series are chiefly argillaceous shales, and they rest upon porphyries and Carboniferous limestone. They have been disturbed and elevated since their deposition. The fossils, which they contain in great number and in a fine state of preservation, will be noticed farther on.All the above mentioned formations were already in existence before the first eruption of the volcanic rocks took place. These latter are found scattered along the whole Pacific coast, and extend from the Gulf of California up to the very summit of the sierra. It is very interesting to see the volcanic formations spread over so extensive a region, especially as there are no active volcanoes known in Northern Mexico, and not even any indications of ancient craters or vents.The lithological character of the eruptive materials is extremely varied, and there seem to have been several periods of igneous action preceded by as many disturbances of the strata, all of which took place after the close of the Cretaceous epoch. Three different series of volcanic rocks may be observed in Sinaloa and Sonora, unconformable with each other; and these may again be subdivided into groups, after a thorough examination has been made of the extensive suite of specimens which has been collected. The lower, or oldest series, affords several hundred varieties of porphyries, characterized by crystals of feldspar or augite. There are also very peculiar trachytic rocks, resembling granite in appearance. These volcanic materials occur in beds or in masses, and are frequently cut by dykes; but they are quite destitute of veins containing gold or silver, the only metalliferous ores they contain being those of copper (?) and iron, and these in small quantity. Various volcanic ridges in Sonora belong to this class. The second series consists of extensive beds of micaceous, trachytic tufas, and breccias, all more or less uplifted since their deposition, and covering the different igneous and sedimentary formations as well as the older volcanic porphyries. These attain a great thickness, between San Dimas and San Ignacio, in Durango and Sinaloa.Above these formations occur ancient alluvial deposits, with bones of extinct animals (elephants) at two localities; near La Noria, northeast of Mazatlan, and in the Arroya de la Palma, two leagues east of La Casita, in Sonora.Sheets of basaltic lavas, somewhat similar to those of California, and probably of the same age, forming with tufas the upper volcanic series, overlie the other formations, occupying a nearly horizontal position.The most recent formation is that of the terrace deposits of sand and gravel, which occur in Sonora.Having thus given a general sketch of the principal groups of rocks developed in the region in question, I pass to a more detailed description of the different formations.Granites.Underlying all the rocks in Durango and Sinaloa, and probably posterior to the Carboniferous limestones, which they have in places extensively metamorphosed, are masses of granite. These may be seen in many places between the coast and San Dimas, either occupying the bottoms of the valleys, or forming independent hills. There are two well-marked varieties: Of these the first are syenites, more or less fine-grained, and consisting of a mixture of feldspar, variously colored, quartz, black or green hornblende, and black or brown mica, the latter usually in hexagonal plates. Localities of this variety are: Haval, Las Higueras, San Ignacio, Santa Apolonia, Candelero, La Noria, Zaragoza, etc., in Sinaloa; San Marcial and Tecoripa valleys, Hermosillo, in Sonora. The other variety is either very coarse-grained, consisting of white feldspar, gray quartz, and plates of silvery mica, or else finer grained, and chiefly made up of feldspar; these occur, forming mountains and ridges in Sonora, in the Sierra del Amolé, near La Magdalena, Sierra del Espinaso Prieto, near Hermosillo, and the Sierra de Mazatan, south of Ures. The fine-grained granites containargentiferous veins at Zaragoza, in Sinaloa, and east of Topisco, in Sonora. These are traversed by numerous intersecting dykes of diorite, feldspar, and quartziferous and feldspathic porphyries, especially well seen near Hermosillo, and the Cajon de los Carrisos, east of San Antonio de la Huerta. There are no metalliferous veins where the granite is thus intersected by dykes.Metalliferous Porphyries.These may be divided into two groups. The first consists of a rock occurring in large irregular masses or beds, and having a dark colored argillaceous base, through which are disseminated small crystals of whitish feldspar. This variety, which is probably older than the granites, includes some of the richest mines of the Sierra Madre; as those of Candelaria, Bolaños, Cinco Señores, etc., near San Dimas, in Durango; and which have yielded over $20,000,000. There are also rich veins in this kind of rock at Candelero, fifty-two leagues northeast of Mazatlan, in Sinaloa. All these veins run northeast and southwest, and are cut at right angles by dykes. The second variety of porphyry is a gray feldspathic rock, apparently made up of labradorite and magnetic iron ore; this overlies the greenstones, and is covered by the Triassic beds at Los Bronces and San Javier, where there are three systems of argentiferous veins. The Nahuila mine, one of the best in Sonora, is in this rock.Metamorphic Rocks.Heavy masses of metamorphic rocks may be seen at various localities in Sinaloa and Durango (Tecomate, Tenchoquelite, Arroyo del Ciruelo, Arroyo de San Vincente) resting either on the granites or the metalliferous porphyries. These rocks occur in masses or beds, sometimes distinctly stratified, and sometimes without any traces of the original bedding. They are always much altered and broken up. Their lithological characters are not well marked, although the series is easily recognized. The rocks referred to in this division, are usually fine-grained, of a greenish or bluish color, when not too much decomposed, and somewhat argillaceous in composition. At the base they pass into porphyries. The argentiferous veins cut both the metamorphic and the porphyritic rocks at Tecomate, on the Rio de San Ignacio, where the dip of the formation is to the northeast, at an angle of 70°. Between La Puerta and El Pilar, Arroyo de San Dimas, they occur in jaspery layers, ribboned with green and brown hues, and resemble some of the metamorphic Triassic rocks of Sonora. Near Candelero, the metamorphic rocks are associated with whitish, semi-crystalline limestone. The formation in question may be observed in many other localities in Sinaloa, always resting on granite and passing into porphyry; it is also sometimes associated with metamorphic slates.Greenstones.These rocks occur in heavy masses or in beds, and are made up of a fine-grained, compact mixture of hornblende and feldspar, often containing mica, and having a greenish color. The greenstone underlies the Triassic rocks, and in many places it protrudes through the granite. This rock is highly metalliferous at Copála, Sinaloa, and also at Los Bronces and San Javier, in Sonora.The greenstones or diorites which occur in the granite, appear to be anterior to the metalliferous greenstones, and the latter are posterior to the Triassic.Carboniferous Limestones.The Carboniferous limestones form high ridges parallel with the general course of the Sierra Madre, from Hermosillo, north of Guaymas, east of Sahuaripa. These ridges become more elevated as we approach the crest of the Sierra. The rocks of this formation are fine-grained and bluish in color, and form heavy beds with intercalated schistose layers; they contain nodules and beds of flint. There are some clay slates at the base of the formation. The thickness of the whole series is probably over five thousand feet. The principal localities where these Carboniferous rocks may be observed are as follows, naming them in order from west to east:1st. Hermosillo, where they rest on syenitic granite and are highly metamorphosed, the limestones being converted into white saccharoidal marble, and the slates into garnet and epidote rock. Dykes of green porphyry cut through the beds of sedimentary rock, which beds have a strike of about N. 65° W., and stand nearly vertical.2d. Five leagues from Hermosillo, at La Cruz; in the Cerro de Santa Teresa on the south, and the Sierra de Las Animas on the north. Here the limestones contain crinoids.3d. Four leagues farther on, between La Noria and El Aguajito; here are high granite ridges with a granite axis.4th. Twenty leagues from Hermosillo, south of Ures; Carboniferous rocks upheaved on the southwest side of the granitic Sierra de Mazatan. The direction of this range is from northwest to southeast, and its height sixteen hundred varas, according to M. De Fleury; here are a few silver mines.5th. Haciendita, nine leagues farther northeast. The beds here are metamorphosed and much disturbed, dipping northeast; these outcrops form low hills.6th. Between Mátape and Batuco; a very high ridge of granite, running in a northerly direction, with limestone resting upon it. To the north and east of Topisco the limestones attain a great thickness and afford fine fossils. At the Cerro de la Bonacina, one of the highest points of the range, a variety of corals, crinoids, and brachiopods may be seen weathered out from the surface of several beds of hard, compact limestone, of various colors; these beds are near the summit of the mountain. This locality was first discovered by Don Antonio Moreno, Engineer of the Bronces mine. The strata here are much disturbed, and appear to have been folded into a mass with a synclinal structure.[23]Triassic Rocks.This formation is usually highly metamorphosed, and passes into porphyriesat its base. The strata are more or less inclined, and the lower beds are very much contorted and disturbed. The rocks referred to the Trias extend from Soyopa to San Javier; but they are developed on a more extensive scale between San Antonio de la Huerta and Los Bronces, forty-two leagues northeast of Guaymas. The Triassic rocks form a chain of high and rugged mountains extending from south-southeast to north-northwest. The isolated mining districts of Tecoripa and San Marcial (between Los Bronces and Guaymas) are in the same formation; it also crops out from under the stratified volcanic rocks at the Punta de Agua, between San Marcial and Guaymas. The metalliferous greenstones and porphyries, previously noticed, form the nucleus around which the Triassic beds have been upheaved. These beds are seen near San Javier and Los Bronces, two mining towns which are situated on greenstone, but which skirt the foot of a small ridge of feldspathic porphyry, much less elevated than the metamorphic rocks themselves. They are also seen overlying granite, near the Cerro Colorado, between Soyopa and Los Bronces, and south of Tecoripa. The Cerro de la Nahuila, the highest point but one in the district, lies southeast of the Sierra de Mazatan. There are three principal divisions of the Triassic, which occur in the following order, the first mentioned being the lowest:1.{Quartzites and clay slates;{Black, jaspery schistose layers;or, where the rocks are less altered:{Black clay shales with beds of coal;{Argillaceous sandstones.2.Quartzites, in great thickness.3.Heavy beds of conglomerate.The interstratified clay shales and grits of the lower member, crop out in several places along the Cañada de Santa Maria, at the bottom of the ravines below Los Bronces. Here, there are three or four beds of good anthracite coal, with a considerable number of well-preserved plants occurring in the associated clay shales, both above and below the coal.[A portion of these plants were referred by me to Dr. Newberry for examination, and he has given the following list of them. 1.Strangerites magnifolia, Rogers; Trans. Assoc. Am. Geologists, p. 306, Pl. xiv. A species occurring in the Trias (?) of Virginia and North Carolina. 2.Pecopteris falcatus, Emmons; Geol. of N. Car., Pl. iv, fig. 9. The specimens are too imperfect to decide on the identity of this plant withSaccopteris germinans. ?3.Pecopteris bullatus, Bunbury; only in fruit; nervation obscure; identity not certain, but very probable. 4.Otozamites Macombii, Newb. At top of “red beds” or “gypsum formation,” at the base of the Cretaceous rocks, copper mines near Abiquiu, New Mexico. There is no doubt about this species, and it forms an important connecting link. ?5.Pterozamites decussatus, Emmons; specimens very imperfect. 6.Pecopteris, n. sp.; a very neat and peculiar species as yet undescribed. It may be the same as one badly figured by Emmons (Pl. II, fig. 1.)7.Alethopteris, n. sp.; small fragments of the frond of a splendid new species. From this enumeration it will be seen that there can be but little doubt of the Triassic age of the formation in which these plants occur. A large lot of these plants, collected by M. Rémond, has been recently received, and among them are much better specimens of some of the species noticed by Dr. Newberry, and several quite new ones. These will also be examined, described, and figured within a short time.J. D. W.]The strike and dip of the clay shales in the different ravines vary considerably, but the dip is usually to the southeast. The superincumbent quartzites are more regular in their inclination. There are dykes of feldspathic rock cutting through both the coal and the shales.The following section represents, in an ascending order, the position of the coal-bearing strata in the Cañon del Retiro, near Los Bronces.1. Coarse quartzites with conglomerates.2. Conglomerate, 8 feet.3. Argillaceous and schistose grits, 3 feet.4. Clay shales, with impressions of plants, 8 feet.5. Gray grits, 4 feet.6. Bluish clay shales with ferns, 12 feet.7. Coal, 2 feet.8. Compact black clay shales, 5 inches.9. Coal, 2 feet 6 inches.10. Clay shales with leaves, several feet.11. Coarse grits.Another section, measured at the foot of the Cerro de la Aguja, was as follows.1. Compact gray grits.2. Gray clay shales with seams of coal and plants, 4 feet 6 inches.3. Bluish argillaceous grits, 2 feet 6 inches.4. Contorted black clay shales, with seams of coal, 5 feet 6 inches.5. Coal, 2 feet 6 inches.6. Black, compact clay shales, 3 feet.7. Coal, 7 inches.8. Carbonaceous clay shales, 8 inches.9. Coal, 3 inches.10. Clay shales and argillaceous grits.[Specimens of the coal brought to San Francisco by M. Rémond, are anthracite, evidently of superior quality.J. D. W.]The middle member of the Triassic series consists of quartzites, or metamorphic sandstones; these are both coarse and fine grained, and sometimes brecciated. They vary in color, from white to red, and are often much altered in the vicinity of the metalliferous veins. The upper member of the series, as seen in the Cañada de la Tinta, is made up of rounded pebbles of black jasper and gray quartzite; in the Cañada de los Mimbres, below Los Bronces pebbles of specular iron are included in the mass. The dip of the formation is very irregular, both in direction and amount.At San Antonio de la Huerta, Tecoripa, and San Marcial, argentiferous veins of various ages occur in the lower and middle members of the Trias. At San Marcial, marine (?) shells are found in the clay slates, near the silver mines;[but those which have been obtained, are too imperfect for recognition; they were referred to Mr. Meek for examination.J. D. W.]At San Marcos, between San Antonio de la Huerta and the Real Viejo, metamorphic jaspery slates occur in connection with the carboniferous limestones; they are probably of Triassic age. Gold is found in the gulches between the quartzite ridges, as in the Cañada de la Higuera, near Los Bronces in the Cañada de la Iglesia, between the latter place and San Antonio de la Huerta, and generally where the quartzites occur.Jurassic (?) Rocks.In the eastern part of the Magdalena and Altar districts, are valleys with low hills and ridges of auriferous clay slates, with interstratified beds of porphyry and diorite. Localities of these rocks are Cerros de la Barajita, between Querobabi and Santa Ana; Cerritos de la Tierra Colorada, where the formation contains beds of variously colored limestones, entirely made up of fossils, South of La Magdalena this formation rests on metamorphic sandstones and shales. [The reasons for referring these rocks, with doubt, to the Jurassic formation, have been already given; see page 246.]Cretaceous Rocks.In the Sahuaripa Valley, four miles east of Arivechi, and seventy-two leagues northeast of Guaymas, is a locality of Cretaceous Fossils of great interest. The hill in which they occur is called “Cerro de las Conchas,” or “Shell Mountain.” The rocks exposed are unfossiliferous strata of coarse-grained sandstone at the base, overlain by clay shales and argillaceous limestone filled with fossils. The exposure is very limited in extent: the shales are a few hundred feet thick, and they dip to the east, as do also the beds of carboniferous limestone on which the Cretaceous deposits rest. Masses of porphyry crop out from under the shales, without there being any peculiar indication of metamorphism or disturbance in their vicinity. Other patches of shelly rock are said to occur in the valley on the eastern side, at the foot of the sierra. [A small lot of fossils collected here by M. Rémond were referred to Mr. Gabb for examination; and since that, a considerable number of additional specimens have been received, but have not yet been investigated. Several species were identified as already described from Texas, and figured by Roemer in “Die Kreidebildungen von Texas;” these are,Ammonites pedernalis, von Buch;Natica pedernalis, Roem.;Turritella seriatim-granulata, Roem.;Gryphæa navis, Hall;Cyphosoma Texanum, Roem.;Eulima Texana, Roem. Besides these, two other species are identified, namely;Cardium multistriatum, Shum., andTurbinolia Texana, Con.There is a considerable number of new species among the specimens from this locality, among which the following genera are represented:Turritella,Chemnitzia,Avellana,Cardium,Trigonia,Panopæa,Pinna,Cucullæa, etc. These will be described and figured by Mr. Gabb, who also remarks that thecharacter of the fossils indicates a closer relationship of the formation to the eastern Cretaceous than to that of California.—J. D. W.]Volcanic Rocks.Stratified volcanic deposits cover a broad area of the surface between San Ignacio and San Dimas (Sinaloa and Durango); they dip to the west. On the other side of Durango they dip in the opposite direction. The serrated edges of the strata may be seen from a great distance, and are extremely picturesque, towering up like old ruins, their peculiar forms being due to erosion. They are well seen in the Cerro de los Frayles, near Guarisamey, in Durango; visible from Mazatlan. These belong to the second series of volcanic rocks. In Sonora there are three different series of volcanic deposits which form serrated, picturesque, parallel ridges, running north from Guaymas as far as La Magdalena, or over eighty leagues in a straight line. The three main ridges, enumerated from west to east, are, 1, Las Tetas de Cabra; 2, Guaymas de Zaragosa; 3, Range north of the mouth of the Yaqui River. The description of the various volcanic deposits of Northern Mexico may be reserved for a separate memoir, as the number of them is very great.Mines.The richest and widest veins are those northeast of Mazatlan, near San Dimas, Guarisamey, etc., in Durango. These veins cut all the rocks older than the Cretaceous, whether igneous or sedimentary. The mines of Sinaloa are richer than those of Sonora. In the former State the ore-bearing portion of the veins is from a few feet to several yards in width: in the latter, generally from one to two feet. In Durango and Sinaloa gold, native silver, and sulphuret of silver occur associated with galena, yellow blende, and iron pyrites. In Sonora the principal ores are argentiferous gray copper, with galena, black blende, copper pyrites, arsenical pyrites, carbonate of lead, ruby silver, arsenical silver, and gold. Each mining district is characterized by a peculiar system of veins; in all as many as twenty different systems have been observed. The most abundant vein stones are quartz, either chalcedonic, crystalline, or massive; brown spar; heavy spar; oxide of iron. The veins occurring in the metamorphic Triassic rocks, are usually parallel with the stratification, so that they lie nearly horizontal where the formation has been but little disturbed. As to the yield of the silver ores, it varies extremely, and it would be necessary to enter into a full description of all the different districts to give an idea of it. It may be noticed, however, that the arsenical pyrites, which is auriferous in the Sierra Nevada, becomes argentiferous in the Sierra Madre. The veins vary in their direction from a little east to a little west of north; the richest ores near San Dimas run northeast and southwest. There are but few rich mines in Sonora, a state of which the mineral wealth has been much exaggerated. There are, however, some deposits of variegated copper, and veins of magnetic and specular iron.The annexed tabular statement will give the principal facts obtained with regard to the mines examined in Northern Mexico.TABULAR STATEMENT,SHOWING THE POSITION AND CHARACTER OF THE PRINCIPAL MINES OF NORTHERN MEXICO.BY A. RÉMOND.—1863-1865.Mines.Location.Country.Strike.Dip.Width.Matrix.Ores.Yield. (Per Ton.)NaghuilaNear San JavierLabrador porphyryN. 35° W.50° N.E.1½ ft.Crystalline quartzSulph’ts of zinc, lead, iron arsenical & copper pyrites; ruby silver & native silver1st class $12002nd class $125EurekaBet. S. Miguelito & Los BroncesGreenstoneN. 45° W.35°-40° .E.QuartzMispickel, blende, galenaPleiteadaNear San JavierLabrador porphyryN. 30° W.45° N.E.1½ ft.QuartzSan JuanNear San JavierQuartzite (triassic)N. 65° E.50° S.S.E.4 ft.Quartz and iron oreGalena, zinc, carbonate of lead, iron pyritesCeballosNear Los BroncesLabrador porphyryN. 25° E.85° S.S.E.2 ft.Magnetic ironHigueraNear Los BroncesGreenstoneN. 5° E.80° E.2½ ft.Magnetic ironCopper pyrites and gray copper oreLa BlancaNear San Antonio de la HuertaQ’tzite and conglom’e (triassic)N. and S.15° E.Vesicular quartzGold and chloro-bromide of silver$43San LuisNear San Antonio de la HuertaQuartzite (triassic)N. 40° W.35° N.E.1½ ft.Decomp. quartz and sulfate of barytaBlende, galena, mispickel, sulphuret of iron, native silver1st class $7872nd class $125Santa BarbaraNear Corral Viejo.QuartziteN.E.-S.W.30° S.E.1½ ft.QuartzGalena, carbonate of lead, iron pyrites, gold$67.75La SierraNear San JavierLabrador porphyryN. 60° E.80° N.N.W.3 ft.Magnetic ironGray copper, iron pyritesSan JoséNear Los BroncesLabrador porphyryN. 27° E.1½ ft.Sulphate of barytaMagnetic iron & iron pyritesEl SecorroNear Los BroncesLabrador porphyryN. 25° E.ZaragozaNear Los BroncesLabrador porphyryN. 23° E.Magnetic ironSan Luis GonzagaNear San JavierLabrador porphyryN. 30° W.30°-40° N.E.8 inchesWhite quartzGalena, blende, mispickel, iron pyritesLa ColoradaNear Los BroncesAltered sandst. & slate (triassic)N. 50° E.80° S.5 ft.Iron ore and quartzAguajitoNear San JavierLabrador porphyryN. 24° E.Magnetic ironSanta EdubigenLa BarrancaQuartzite (triassic)N.E.-S.W.30° N.W.2½ ft.QuartzLa CuadraNear San JavierLabrador porphyryN. 10° W.20°-25° E.1 ft.QuartzArsenical pyrites, blende, and galenaEl RosarioNear San JavierLabrador porphyryN. 10° W.20°-25° E.Crystalline quartzEl EscritorioNear San JavierLabrador porphyryN.W.-S.E.N.E.1½ ft.White quartzSanta RosaBet. Los Bronces and San JavierQuartzite (triassic)N. 10° E.55° S.3 ft.Quartz and iron oreCarbonate of lead, iron ore, galena, blende, iron pyritesSoledadCandeleroPorphyry (metam.)N. 55° E.85° S.E.30 ft.Quartz$266.65CarmenCandeleroPorphyry (metam.)N. 85° E.85° N.28 ft.QuartzSilver and gold, sulph. of silver$186.65AtochaCandeleroPorphyry (metam.)N. 45° E.85° N.14 ft.QuartzSilver and gold, sulph. of silver$213.35RosarioCandeleroPorphyry (metam.)N. 50° E.70° to 80° N.W.17 ft.Silver and gold, sulph. of silver$160ContrestacaNear La PuertaMetamorphic rocksN. 63° E.76° N.W.White quartzBlende, galena, sulph. of silverDescubridoraNear La PuertaMetamorphic rocksN. 35° E.69° N.W.White quartzBlende, galena, sulph. of silverSoledadBet. La Puerta and San DimasMetamorphic rocksN. 65° E.Perp.White quartzBlende, galena, sulph. of silverCandelariaNear San DimasPorphyry (metam.)N. 63° E.63° N.N.W.White quartz1st class $32102d class $ 133BolanosNear San DimasPorphyry (metam.)N. 45° E.75° S.E.20 ft.White quartzGalenaCinco de MayoNear ZaragozaSyenitic graniteN. 52° E.75° N.W.4 ft.White quartzGalena, blende, iron pyrites, brittle silver glance, native silver1st class $8002d class $180Cinco SeñoresNear CopálaGreenstoneN. 20° W.45° E.N.E.1 to 4 ft.QuartzGalena, blende, iron pyritesNapoleonNear CopálaGreenstoneN. 10° W.80° E.2 to 8 ft.Chalcedonic quartzGalena, blende, copper pyrites, etc.RosarioNear CopálaGreenstoneN. 50° W.85° E.Chalcedonic quartzPatinoNear CopálaGreenstoneN. 22° W.Perp.4 ft.Chalcedonic quartzGalena, blende, copper pyritesHavalA few leagues from MazatlanSyenitic graniteN. 80° E.80° N.QuartzOxide of lead, native silverMina GrandeNear San MarcialMetamorphic slates (triassic)N. and S.30° W.2 ft.QuartzSulphuret of antimony, mispickel, copper pyrites, blende, iron pyritesLas CruzecitasNear San MarcialMetamorphic slates (triassic)N. 15° E.65° E.4½ ft.Heavy sparTepustete with copper and iron pyrites, and gray copper ore1st cl. $90-1002d cl. $35-40Guijosita ViejaNear San JavierLabrador porphyryQuartzGalena, arsenical pyrites, blende, copper pyritesLa AntimoniaNear San JavierLabrador porphyryCrystalline quartzSulphuret of antimony and leadDios PadreTrinidadLabrador porphyry9 to 12 ft. of oreGray copper ore, galena, iron pyrites, native silverAgua Grande9 miles from San MarcialPorphyry (volcanic)N. 38°-40° E.80° N.W.1½ ft.White quartzIndigo copper, chrysocolla, chalkosine, chalcopyriteLa ColoradaNear CopálaGreenstoneN. and S.20° W.40 ft.Chalcedonic quartzAlgodonaNear San MarcialMetamorphic slates (triassic)N. and S.30° W.8 inchesRotten quartz and iron oreChlorobromide of silverLos BroncesLos BroncesGreenstoneE. of N.85° E.Heavy sparMagnetic iron, gray copper, copper and iron pyrites1st class $3502d class $40-60La PrietaLos BroncesGreenstoneN. 40° E.80° N.W.Heavy sparMagnetic iron, gray copper, copper and iron pyritesAlta GraciaNear San Antonio de la HuertaQuartzite (triassic).N. and S.30° E.4 ft.Brown sparCopper pyrites and gray copperRosario de GuadalupeSan JavierGreenstoneN. 70° E.60° S.S.E.2 ft.QuartzBlack blende, iron pyrites and galenaAuroraNear Los BroncesGreenstoneN. 10° E.45-50° E.2 ft.Magnetic ironGray copper ore and copper pyritesEl TasteNear San JavierGreenstoneN. 15° E.50-55° E.5 ft.QuartzGalena, blende, copper and iron pyrites (petanque)$100ProvidenciaNear TecoripaQuartzite (triassic)N. 10° E.65° E.1 ft. 2 in.Quartz1st class $2002d cl. $35-40La BojorqueñaNear TecoripaQuartzite (triassic)N. 20° E.65° E.Quartz (ferruginous)Black blende, iron pyrites, galena, copper pyritesLa ChipioñenaNear TopiscoGraniteMina PrietaNear San Antonio de la HuertaQuartzite (triassic)Brown sparCopper pyrites, gray copperEl TesoroCacachilasGraniteN.W.-S.E.75° S.W.4 ft.1st class $2202d class $90RosarioCañada de la Iglesia, near San AntonioQuartzite (triassic).N.E.-S.W.85° N.W.2 ft.Galena and blende$60BabicanoraLimestone (carboniferous)N.E.-S.W.75° N.W.5 ft.QuartzGalena, iron pyrites, fahlerz, ruby silver ore; gold and silver$34.65[21]The best map of Northern Mexico is that of M. de Fleury, published in San Francisco, in 1864; but this makes little pretense to a delineation of the topography; the courses of the principal streams and the position of the larger mining towns are often very far from being correct, as must be expected on a map constructed without a basis of instrumental surveys.J. D. W.[22]See Emory, in Mexican Boundary Report, vol. 1, page 41.[23]Only a few specimens of the Carboniferous fossils collected by M. Rémond have ever been received, owing to circumstances connected with the present political condition of Mexico. It is hoped, however, that they are not lost, and that they may yet be recovered. Among the few specimens received is a coral, not to be distinguished from theLithostrotion(L. mamillare) found near Bass’s Ranch, in Shasta County, California.J. D. W.
BY A. RÉMOND.
[Compiled from his notes, and prepared for publication, by J. D. Whitney.]
The mountainous region comprising the central and western portion of Northern Mexico, belongs to the four States of Durango, Chihuahua, Sinaloa, and Sonora. Considering how celebrated this portion of Mexico has become for its mines and metalliferous veins, and how much has been written about it, it is surprising how little exact information has hitherto been obtained with regard to either its geography or geology. On comparing the principal published maps[21]of the region in question, it will be seen at once how much they differ from each other in their delineations of even its main topographical features, while the details are entirely wanting.
The name of the “Sierra Madre” is usually applied to the main range of mountains of this country, or the western border of the plateau which stretches north through the territories of the United States, forming what may be called the great orographical feature of the continent. In Northwestern Mexico this crumpled border of the great plateau comprises an extensive mountainous region, by no means forming a continuous single chain, but rather several central ranges, with associated groups of parallel ridges, all having the same general course, which is approximately north-northwest, and south-southeast. As the breadth of the chain widens as we go towards the north, so, too, that of the valleys increases in that direction, the whole system of mountains and valleys spreading out in something like a fan shape.
Going north, the chain appears to sink gradually, although determinations of altitude in Northern Mexico are extremely few in number. It is certain that there is, in about latitude 32°, a depression of the mountain ranges which extends entirely across the continent, and which would enable the traveler to cross from the Atlantic to the Pacific, without necessarily surmounting any elevation greater than four thousand feet.[22]The southeastern range is the highest, and the culminating point is said to be the Cerro de Cuiteco, sixty leagues northeast of Jesus Maria, on the western border of Chihuahua. The approximate altitude of the Cumbre de Basascachic is seven thousand four hundred and twenty-nine feet, and that of Guadalupe y Calvo, seven thousand eight hundred and twenty-five feet. To the north, the ranges east of Sahuaripa are also very high; but they have never been measured. No peaks or ridges, however, in this portion of Mexico attain anything like the elevation of the higher portion of the Sierra Nevada, few if any points exceeding ten thousand feet in altitude.
The direction of the sierra is nearly that of a line connecting some of the best mining districts in Mexico, which are situated on or very near the summit of the mountains. These districts are the following, enumerating them in their geographical order from the south towards the north: In Durango, San Antonio de las Ventanas, Guarisamey, and San Dimas, remarkable for their auriferous silver ores, and sixty-two Mexican leagues northeast of Mazatlan; in Chihuahua, Guadalupe y Calvo, and San Pedro de Batopilas, yielding fine specimens of native silver; also, Jesus Maria, in the same State, and the Real del la Cieneguita, Sonora, with silver and gold mines.
The geological structure of the occidental slope of the Sierra Madre, as well as that of the other parts of this great chain, is exceedingly interesting, and, as yet but very little known, notwithstanding the valuable investigations of Humboldt and other eminent men; for, up to the present time, the age of the different formations has never been fixed with any degree of accuracy, from want of materials and of sufficient observations. In 1863, 1864, and 1865, however, I explored quite a number of localities in northwestern Mexico, and was thusenabled to obtain a pretty good general idea of the geology of that region; and, in Sonora, to which my attention was especially devoted, I succeeded in finding fossils in sufficient quantity to allow of the determination of the age of the principal formations of the northern Sierra Madre. By tracing the connection of these rocks with those of Central Mexico, additional light will be thrown on those districts of which, at present, but little is definitely known.
The igneous rocks, which occur more abundantly on the Pacific slope, are granites, either fine or very coarse-grained; porphyries, more or less feldspathic; and greenstones, all of which are cut by numerous dykes of extremely varied character. The granites, however, are very poor in veins of the precious metals, while the porphyries are highly metalliferous. In Sinaloa (Candelero) and Durango (San Dimas) we see that the granites underlie the metalliferous porphyries, and that the greenstones, in Sonora, (near Hermosillo and in the vicinity of La Haciendita) penetrate through them.
The oldest sedimentary rocks, which I have observed, belong to the Carboniferous series; this is represented in the eastern part of Sonora, by heavy masses of limestone, forming very high and rugged ridges, running a little west of north. The upturned strata are seen, in many places, to rest on granite. Argentiferous veins occur throughout this formation.
The next group of sedimentary rocks, in order, is the Triassic; this forms isolated mountain groups in Sonora, and offers an interesting field for investigation. Instead of limestones, it is made up of heavy beds of quartzites and conglomerates, with coal-bearing clay shales; all of these are disturbed and elevated, and rest on greenstones, feldspathic porphyries, or granite. Wherever metamorphosed, the Triassic rocks are auriferous and contain veins of silver ores. The metamorphic slates and limestones of the Altar and Magdalena districts, which include the richest gold placers of Sonora, may possibly be of Triassic age; but the fossils collected are too imperfect to admit of this being determined. There are some reasons for believing those rocks to be rather of Jurassic than of Triassic age, as they differ in lithological characters from both the Triassic and Carboniferous of Northern Mexico, resembling, rather, the Jurassic gold-bearing slates of the Sierra Nevada, in California; besides, they lie outside and to the west of the Sierra Madre. It may also be noticed that the gold which they furnish does not resemble that obtained from the Triassic strata.
The Cretaceous period is also represented at the foot of the Sierra Madre, at Arivechi, in Sonora. The strata belonging to this series are chiefly argillaceous shales, and they rest upon porphyries and Carboniferous limestone. They have been disturbed and elevated since their deposition. The fossils, which they contain in great number and in a fine state of preservation, will be noticed farther on.
All the above mentioned formations were already in existence before the first eruption of the volcanic rocks took place. These latter are found scattered along the whole Pacific coast, and extend from the Gulf of California up to the very summit of the sierra. It is very interesting to see the volcanic formations spread over so extensive a region, especially as there are no active volcanoes known in Northern Mexico, and not even any indications of ancient craters or vents.
The lithological character of the eruptive materials is extremely varied, and there seem to have been several periods of igneous action preceded by as many disturbances of the strata, all of which took place after the close of the Cretaceous epoch. Three different series of volcanic rocks may be observed in Sinaloa and Sonora, unconformable with each other; and these may again be subdivided into groups, after a thorough examination has been made of the extensive suite of specimens which has been collected. The lower, or oldest series, affords several hundred varieties of porphyries, characterized by crystals of feldspar or augite. There are also very peculiar trachytic rocks, resembling granite in appearance. These volcanic materials occur in beds or in masses, and are frequently cut by dykes; but they are quite destitute of veins containing gold or silver, the only metalliferous ores they contain being those of copper (?) and iron, and these in small quantity. Various volcanic ridges in Sonora belong to this class. The second series consists of extensive beds of micaceous, trachytic tufas, and breccias, all more or less uplifted since their deposition, and covering the different igneous and sedimentary formations as well as the older volcanic porphyries. These attain a great thickness, between San Dimas and San Ignacio, in Durango and Sinaloa.
Above these formations occur ancient alluvial deposits, with bones of extinct animals (elephants) at two localities; near La Noria, northeast of Mazatlan, and in the Arroya de la Palma, two leagues east of La Casita, in Sonora.
Sheets of basaltic lavas, somewhat similar to those of California, and probably of the same age, forming with tufas the upper volcanic series, overlie the other formations, occupying a nearly horizontal position.
The most recent formation is that of the terrace deposits of sand and gravel, which occur in Sonora.
Having thus given a general sketch of the principal groups of rocks developed in the region in question, I pass to a more detailed description of the different formations.
Underlying all the rocks in Durango and Sinaloa, and probably posterior to the Carboniferous limestones, which they have in places extensively metamorphosed, are masses of granite. These may be seen in many places between the coast and San Dimas, either occupying the bottoms of the valleys, or forming independent hills. There are two well-marked varieties: Of these the first are syenites, more or less fine-grained, and consisting of a mixture of feldspar, variously colored, quartz, black or green hornblende, and black or brown mica, the latter usually in hexagonal plates. Localities of this variety are: Haval, Las Higueras, San Ignacio, Santa Apolonia, Candelero, La Noria, Zaragoza, etc., in Sinaloa; San Marcial and Tecoripa valleys, Hermosillo, in Sonora. The other variety is either very coarse-grained, consisting of white feldspar, gray quartz, and plates of silvery mica, or else finer grained, and chiefly made up of feldspar; these occur, forming mountains and ridges in Sonora, in the Sierra del Amolé, near La Magdalena, Sierra del Espinaso Prieto, near Hermosillo, and the Sierra de Mazatan, south of Ures. The fine-grained granites containargentiferous veins at Zaragoza, in Sinaloa, and east of Topisco, in Sonora. These are traversed by numerous intersecting dykes of diorite, feldspar, and quartziferous and feldspathic porphyries, especially well seen near Hermosillo, and the Cajon de los Carrisos, east of San Antonio de la Huerta. There are no metalliferous veins where the granite is thus intersected by dykes.
These may be divided into two groups. The first consists of a rock occurring in large irregular masses or beds, and having a dark colored argillaceous base, through which are disseminated small crystals of whitish feldspar. This variety, which is probably older than the granites, includes some of the richest mines of the Sierra Madre; as those of Candelaria, Bolaños, Cinco Señores, etc., near San Dimas, in Durango; and which have yielded over $20,000,000. There are also rich veins in this kind of rock at Candelero, fifty-two leagues northeast of Mazatlan, in Sinaloa. All these veins run northeast and southwest, and are cut at right angles by dykes. The second variety of porphyry is a gray feldspathic rock, apparently made up of labradorite and magnetic iron ore; this overlies the greenstones, and is covered by the Triassic beds at Los Bronces and San Javier, where there are three systems of argentiferous veins. The Nahuila mine, one of the best in Sonora, is in this rock.
Heavy masses of metamorphic rocks may be seen at various localities in Sinaloa and Durango (Tecomate, Tenchoquelite, Arroyo del Ciruelo, Arroyo de San Vincente) resting either on the granites or the metalliferous porphyries. These rocks occur in masses or beds, sometimes distinctly stratified, and sometimes without any traces of the original bedding. They are always much altered and broken up. Their lithological characters are not well marked, although the series is easily recognized. The rocks referred to in this division, are usually fine-grained, of a greenish or bluish color, when not too much decomposed, and somewhat argillaceous in composition. At the base they pass into porphyries. The argentiferous veins cut both the metamorphic and the porphyritic rocks at Tecomate, on the Rio de San Ignacio, where the dip of the formation is to the northeast, at an angle of 70°. Between La Puerta and El Pilar, Arroyo de San Dimas, they occur in jaspery layers, ribboned with green and brown hues, and resemble some of the metamorphic Triassic rocks of Sonora. Near Candelero, the metamorphic rocks are associated with whitish, semi-crystalline limestone. The formation in question may be observed in many other localities in Sinaloa, always resting on granite and passing into porphyry; it is also sometimes associated with metamorphic slates.
These rocks occur in heavy masses or in beds, and are made up of a fine-grained, compact mixture of hornblende and feldspar, often containing mica, and having a greenish color. The greenstone underlies the Triassic rocks, and in many places it protrudes through the granite. This rock is highly metalliferous at Copála, Sinaloa, and also at Los Bronces and San Javier, in Sonora.The greenstones or diorites which occur in the granite, appear to be anterior to the metalliferous greenstones, and the latter are posterior to the Triassic.
The Carboniferous limestones form high ridges parallel with the general course of the Sierra Madre, from Hermosillo, north of Guaymas, east of Sahuaripa. These ridges become more elevated as we approach the crest of the Sierra. The rocks of this formation are fine-grained and bluish in color, and form heavy beds with intercalated schistose layers; they contain nodules and beds of flint. There are some clay slates at the base of the formation. The thickness of the whole series is probably over five thousand feet. The principal localities where these Carboniferous rocks may be observed are as follows, naming them in order from west to east:
1st. Hermosillo, where they rest on syenitic granite and are highly metamorphosed, the limestones being converted into white saccharoidal marble, and the slates into garnet and epidote rock. Dykes of green porphyry cut through the beds of sedimentary rock, which beds have a strike of about N. 65° W., and stand nearly vertical.
2d. Five leagues from Hermosillo, at La Cruz; in the Cerro de Santa Teresa on the south, and the Sierra de Las Animas on the north. Here the limestones contain crinoids.
3d. Four leagues farther on, between La Noria and El Aguajito; here are high granite ridges with a granite axis.
4th. Twenty leagues from Hermosillo, south of Ures; Carboniferous rocks upheaved on the southwest side of the granitic Sierra de Mazatan. The direction of this range is from northwest to southeast, and its height sixteen hundred varas, according to M. De Fleury; here are a few silver mines.
5th. Haciendita, nine leagues farther northeast. The beds here are metamorphosed and much disturbed, dipping northeast; these outcrops form low hills.
6th. Between Mátape and Batuco; a very high ridge of granite, running in a northerly direction, with limestone resting upon it. To the north and east of Topisco the limestones attain a great thickness and afford fine fossils. At the Cerro de la Bonacina, one of the highest points of the range, a variety of corals, crinoids, and brachiopods may be seen weathered out from the surface of several beds of hard, compact limestone, of various colors; these beds are near the summit of the mountain. This locality was first discovered by Don Antonio Moreno, Engineer of the Bronces mine. The strata here are much disturbed, and appear to have been folded into a mass with a synclinal structure.[23]
This formation is usually highly metamorphosed, and passes into porphyriesat its base. The strata are more or less inclined, and the lower beds are very much contorted and disturbed. The rocks referred to the Trias extend from Soyopa to San Javier; but they are developed on a more extensive scale between San Antonio de la Huerta and Los Bronces, forty-two leagues northeast of Guaymas. The Triassic rocks form a chain of high and rugged mountains extending from south-southeast to north-northwest. The isolated mining districts of Tecoripa and San Marcial (between Los Bronces and Guaymas) are in the same formation; it also crops out from under the stratified volcanic rocks at the Punta de Agua, between San Marcial and Guaymas. The metalliferous greenstones and porphyries, previously noticed, form the nucleus around which the Triassic beds have been upheaved. These beds are seen near San Javier and Los Bronces, two mining towns which are situated on greenstone, but which skirt the foot of a small ridge of feldspathic porphyry, much less elevated than the metamorphic rocks themselves. They are also seen overlying granite, near the Cerro Colorado, between Soyopa and Los Bronces, and south of Tecoripa. The Cerro de la Nahuila, the highest point but one in the district, lies southeast of the Sierra de Mazatan. There are three principal divisions of the Triassic, which occur in the following order, the first mentioned being the lowest:
The interstratified clay shales and grits of the lower member, crop out in several places along the Cañada de Santa Maria, at the bottom of the ravines below Los Bronces. Here, there are three or four beds of good anthracite coal, with a considerable number of well-preserved plants occurring in the associated clay shales, both above and below the coal.
[A portion of these plants were referred by me to Dr. Newberry for examination, and he has given the following list of them. 1.Strangerites magnifolia, Rogers; Trans. Assoc. Am. Geologists, p. 306, Pl. xiv. A species occurring in the Trias (?) of Virginia and North Carolina. 2.Pecopteris falcatus, Emmons; Geol. of N. Car., Pl. iv, fig. 9. The specimens are too imperfect to decide on the identity of this plant withSaccopteris germinans. ?3.Pecopteris bullatus, Bunbury; only in fruit; nervation obscure; identity not certain, but very probable. 4.Otozamites Macombii, Newb. At top of “red beds” or “gypsum formation,” at the base of the Cretaceous rocks, copper mines near Abiquiu, New Mexico. There is no doubt about this species, and it forms an important connecting link. ?5.Pterozamites decussatus, Emmons; specimens very imperfect. 6.Pecopteris, n. sp.; a very neat and peculiar species as yet undescribed. It may be the same as one badly figured by Emmons (Pl. II, fig. 1.)7.Alethopteris, n. sp.; small fragments of the frond of a splendid new species. From this enumeration it will be seen that there can be but little doubt of the Triassic age of the formation in which these plants occur. A large lot of these plants, collected by M. Rémond, has been recently received, and among them are much better specimens of some of the species noticed by Dr. Newberry, and several quite new ones. These will also be examined, described, and figured within a short time.J. D. W.]
The strike and dip of the clay shales in the different ravines vary considerably, but the dip is usually to the southeast. The superincumbent quartzites are more regular in their inclination. There are dykes of feldspathic rock cutting through both the coal and the shales.
The following section represents, in an ascending order, the position of the coal-bearing strata in the Cañon del Retiro, near Los Bronces.
Another section, measured at the foot of the Cerro de la Aguja, was as follows.
[Specimens of the coal brought to San Francisco by M. Rémond, are anthracite, evidently of superior quality.J. D. W.]
The middle member of the Triassic series consists of quartzites, or metamorphic sandstones; these are both coarse and fine grained, and sometimes brecciated. They vary in color, from white to red, and are often much altered in the vicinity of the metalliferous veins. The upper member of the series, as seen in the Cañada de la Tinta, is made up of rounded pebbles of black jasper and gray quartzite; in the Cañada de los Mimbres, below Los Bronces pebbles of specular iron are included in the mass. The dip of the formation is very irregular, both in direction and amount.
At San Antonio de la Huerta, Tecoripa, and San Marcial, argentiferous veins of various ages occur in the lower and middle members of the Trias. At San Marcial, marine (?) shells are found in the clay slates, near the silver mines;[but those which have been obtained, are too imperfect for recognition; they were referred to Mr. Meek for examination.J. D. W.]
At San Marcos, between San Antonio de la Huerta and the Real Viejo, metamorphic jaspery slates occur in connection with the carboniferous limestones; they are probably of Triassic age. Gold is found in the gulches between the quartzite ridges, as in the Cañada de la Higuera, near Los Bronces in the Cañada de la Iglesia, between the latter place and San Antonio de la Huerta, and generally where the quartzites occur.
In the eastern part of the Magdalena and Altar districts, are valleys with low hills and ridges of auriferous clay slates, with interstratified beds of porphyry and diorite. Localities of these rocks are Cerros de la Barajita, between Querobabi and Santa Ana; Cerritos de la Tierra Colorada, where the formation contains beds of variously colored limestones, entirely made up of fossils, South of La Magdalena this formation rests on metamorphic sandstones and shales. [The reasons for referring these rocks, with doubt, to the Jurassic formation, have been already given; see page 246.]
In the Sahuaripa Valley, four miles east of Arivechi, and seventy-two leagues northeast of Guaymas, is a locality of Cretaceous Fossils of great interest. The hill in which they occur is called “Cerro de las Conchas,” or “Shell Mountain.” The rocks exposed are unfossiliferous strata of coarse-grained sandstone at the base, overlain by clay shales and argillaceous limestone filled with fossils. The exposure is very limited in extent: the shales are a few hundred feet thick, and they dip to the east, as do also the beds of carboniferous limestone on which the Cretaceous deposits rest. Masses of porphyry crop out from under the shales, without there being any peculiar indication of metamorphism or disturbance in their vicinity. Other patches of shelly rock are said to occur in the valley on the eastern side, at the foot of the sierra. [A small lot of fossils collected here by M. Rémond were referred to Mr. Gabb for examination; and since that, a considerable number of additional specimens have been received, but have not yet been investigated. Several species were identified as already described from Texas, and figured by Roemer in “Die Kreidebildungen von Texas;” these are,Ammonites pedernalis, von Buch;Natica pedernalis, Roem.;Turritella seriatim-granulata, Roem.;Gryphæa navis, Hall;Cyphosoma Texanum, Roem.;Eulima Texana, Roem. Besides these, two other species are identified, namely;Cardium multistriatum, Shum., andTurbinolia Texana, Con.
There is a considerable number of new species among the specimens from this locality, among which the following genera are represented:Turritella,Chemnitzia,Avellana,Cardium,Trigonia,Panopæa,Pinna,Cucullæa, etc. These will be described and figured by Mr. Gabb, who also remarks that thecharacter of the fossils indicates a closer relationship of the formation to the eastern Cretaceous than to that of California.—J. D. W.]
Stratified volcanic deposits cover a broad area of the surface between San Ignacio and San Dimas (Sinaloa and Durango); they dip to the west. On the other side of Durango they dip in the opposite direction. The serrated edges of the strata may be seen from a great distance, and are extremely picturesque, towering up like old ruins, their peculiar forms being due to erosion. They are well seen in the Cerro de los Frayles, near Guarisamey, in Durango; visible from Mazatlan. These belong to the second series of volcanic rocks. In Sonora there are three different series of volcanic deposits which form serrated, picturesque, parallel ridges, running north from Guaymas as far as La Magdalena, or over eighty leagues in a straight line. The three main ridges, enumerated from west to east, are, 1, Las Tetas de Cabra; 2, Guaymas de Zaragosa; 3, Range north of the mouth of the Yaqui River. The description of the various volcanic deposits of Northern Mexico may be reserved for a separate memoir, as the number of them is very great.
The richest and widest veins are those northeast of Mazatlan, near San Dimas, Guarisamey, etc., in Durango. These veins cut all the rocks older than the Cretaceous, whether igneous or sedimentary. The mines of Sinaloa are richer than those of Sonora. In the former State the ore-bearing portion of the veins is from a few feet to several yards in width: in the latter, generally from one to two feet. In Durango and Sinaloa gold, native silver, and sulphuret of silver occur associated with galena, yellow blende, and iron pyrites. In Sonora the principal ores are argentiferous gray copper, with galena, black blende, copper pyrites, arsenical pyrites, carbonate of lead, ruby silver, arsenical silver, and gold. Each mining district is characterized by a peculiar system of veins; in all as many as twenty different systems have been observed. The most abundant vein stones are quartz, either chalcedonic, crystalline, or massive; brown spar; heavy spar; oxide of iron. The veins occurring in the metamorphic Triassic rocks, are usually parallel with the stratification, so that they lie nearly horizontal where the formation has been but little disturbed. As to the yield of the silver ores, it varies extremely, and it would be necessary to enter into a full description of all the different districts to give an idea of it. It may be noticed, however, that the arsenical pyrites, which is auriferous in the Sierra Nevada, becomes argentiferous in the Sierra Madre. The veins vary in their direction from a little east to a little west of north; the richest ores near San Dimas run northeast and southwest. There are but few rich mines in Sonora, a state of which the mineral wealth has been much exaggerated. There are, however, some deposits of variegated copper, and veins of magnetic and specular iron.
The annexed tabular statement will give the principal facts obtained with regard to the mines examined in Northern Mexico.
BY A. RÉMOND.—1863-1865.
[21]The best map of Northern Mexico is that of M. de Fleury, published in San Francisco, in 1864; but this makes little pretense to a delineation of the topography; the courses of the principal streams and the position of the larger mining towns are often very far from being correct, as must be expected on a map constructed without a basis of instrumental surveys.J. D. W.[22]See Emory, in Mexican Boundary Report, vol. 1, page 41.[23]Only a few specimens of the Carboniferous fossils collected by M. Rémond have ever been received, owing to circumstances connected with the present political condition of Mexico. It is hoped, however, that they are not lost, and that they may yet be recovered. Among the few specimens received is a coral, not to be distinguished from theLithostrotion(L. mamillare) found near Bass’s Ranch, in Shasta County, California.J. D. W.
[21]The best map of Northern Mexico is that of M. de Fleury, published in San Francisco, in 1864; but this makes little pretense to a delineation of the topography; the courses of the principal streams and the position of the larger mining towns are often very far from being correct, as must be expected on a map constructed without a basis of instrumental surveys.J. D. W.
[21]The best map of Northern Mexico is that of M. de Fleury, published in San Francisco, in 1864; but this makes little pretense to a delineation of the topography; the courses of the principal streams and the position of the larger mining towns are often very far from being correct, as must be expected on a map constructed without a basis of instrumental surveys.J. D. W.
[22]See Emory, in Mexican Boundary Report, vol. 1, page 41.
[22]See Emory, in Mexican Boundary Report, vol. 1, page 41.
[23]Only a few specimens of the Carboniferous fossils collected by M. Rémond have ever been received, owing to circumstances connected with the present political condition of Mexico. It is hoped, however, that they are not lost, and that they may yet be recovered. Among the few specimens received is a coral, not to be distinguished from theLithostrotion(L. mamillare) found near Bass’s Ranch, in Shasta County, California.J. D. W.
[23]Only a few specimens of the Carboniferous fossils collected by M. Rémond have ever been received, owing to circumstances connected with the present political condition of Mexico. It is hoped, however, that they are not lost, and that they may yet be recovered. Among the few specimens received is a coral, not to be distinguished from theLithostrotion(L. mamillare) found near Bass’s Ranch, in Shasta County, California.J. D. W.
President in the Chair.
Twelve members present.
Donations to the Cabinet: Sections of theSequoia giganteaand a roll showing the annual growth of the “Old Maid,” one of the trees in the Calaveras grove of Big Trees; from Mr. Henry Hentsch.
Mr. Dall stated that Dr. Cooper had discovered, in the vicinity of Santa Cruz,Helix redemita,H. Vancouverensis,H. Columbiana, andH. arrosa; also, in the small rivulets near the town,Margaritana falcata, besides several univalves, and also an undeterminedHelix, which may prove to be new. Mr. Dall also remarked that Rev. J. Rowell had obtained at Hayward’s, Alameda County, a number of specimens ofHelix Cronkhitei, which is a new locality for that species.
Mr. Dall remarked that in dissecting a specimen ofTrochiscus Norrissii, the position of which has for some time been doubtful, sufficient evidence was obtained to decide that it did not belong with the Proboscidians, to which group it had been doubtfully referred by several naturalists.
Mr. Stearns in the Chair.
Five members present.
Mr. Bloomer presented some Diatoms, from the coast of California, supposed to belong to the generaMelissaandMeridion; they were both found growing upon calcareous sea weeds. The genusMeridionhas not heretofore been recorded as occurring in California.
Mr. Dall presented, in the name of Dr. Cooper, the following paper: