Fig. 383.Holoptychius Hibberti, Ag. Fifeshire coal-field; natural size.
Fig. 383.
Holoptychius Hibberti, Ag. Fifeshire coal-field; natural size.
The annexed figure represents a large tooth of theMegalichthys, found by Mr. Horner in the Cannel coal of Fifeshire. It probably inhabited an estuary, like many of its contemporaries, and frequented both rivers and the sea.
Fig. 384.Archegosaurus minor,Goldfuss. Fossilreptile from the coal-measures, Saarbrück.
Fig. 384.
Archegosaurus minor,Goldfuss. Fossilreptile from the coal-measures, Saarbrück.
At length, in 1844, the first skeleton of a true reptile was announced from the coal of Münster-Appel in Rhenish Bavaria, by H. von Meyer, under the name ofApateon pedestris, the animal being supposed to be nearly related to the salamanders. Three years later, in 1847, Prof. von Dechen found in the coal-field of Saarbrück, at the village of Lebach, between Strasburg and Treves, the skeletons of no less than three distinct species of air-breathing reptiles, which were described by the late Prof. Goldfuss under the generic name ofArchegosaurus. The ichthyolites and plants found in the same strata, left no doubt that these remains belonged to the true coal period. The skulls, teeth, and the greater portions of the skeleton, nay, even a large part of the skin, of two of these reptiles have been faithfully preserved in the centreof spheroidal concretions of clay-iron-stone. The largest of these lizards,Archegosaurus Decheni, must have been 3 feet 6 inches long. The annexed drawing represents the smallest of the three of the natural size. They were considered by Goldfuss as saurians, but by Herman von Meyer as most nearly allied to theLabyrinthodon, and therefore connected with the batrachians, as well as the lizards. The remains of the extremities leave no doubt that they were quadrupeds, "provided," says Von Meyer, "with hands and feet terminating in distinct toes; but these limbs were weak, serving only for swimming or creeping." The same anatomist has pointed out certain points of analogy between their bones and those of theProteus anguinus; and Mr. Owen has observed to me that they make an approach to theProteusin the shortness of their ribs. Two of these ancient reptiles retain a large part of the outer skin, which consisted of long, narrow, wedge-shaped, tile-like, and horny scales, arranged in rows (seefig. 385.).
Fig. 385.Imbricated covering of skin ofArchegosaurus medius, Goldf.; magnified.[337-A]
Fig. 385.
Imbricated covering of skin ofArchegosaurus medius, Goldf.; magnified.[337-A]
Cheirotherian footprints in coal measures, United States.—In 1844, the very year when the Apateon or Salamander of the coal was first met with in the country between the Moselle and the Rhine, Dr. King published an account of the footprints of a large reptile discovered by him in North America. These occur in the coal strata of Greensburg, in Westmoreland County, Pennsylvania; and I had an opportunity of examining them in 1846. I was at once convinced of their genuineness, and declared my conviction on that point, on which doubts had been entertained both in Europe and the United States. The footmarks were first observed standing out in relief from the lower surface of slabs of sandstone, resting on thin layers of fine unctuous clay. I brought away one of these masses, which is represented in the accompanying drawing (fig. 386.). It displays, together with footprints, the casts of cracks (a,a') of various sizes. The origin of such cracks in clay, and casts of the same, has before been explained, and referred to the drying and shrinking of mud, and the subsequent pouring of sand into open crevices. It will be seen that some of the cracks, as atb,c, traverse the footprints, and produce distortion in them, as might have been expected, for the mud must have been soft when the animal walked over it and left the impressions; whereas, when it afterwards dried up and shrank, it would be too hard to receive such indentations.
No less than twenty-three footsteps were observed by Dr. King in the same quarry before it was abandoned, the greater part of them so arranged (seefig. 387.) on the surface of one stratum as to imply that they were made successively by the same animal. Everywhere there was a double row of tracks, and in each row they occur inpairs, each pair consisting of a hind and fore foot, and each being at nearly equal distances from the next pair. In each parallel row the toes turn the one set to the right, the other to the left. In the EuropeanCheirotherium, before mentioned (p. 290.), both the hind and fore feet have each five toes, and the size of the hind foot is about five times as large as the fore foot. In the American fossil the posterior footprint is not even twice as large as the anterior, and the number of toes is unequal, being five in the hinder and four in the anterior foot. In this, as in the EuropeanCheirotherium, one toe stands out like a thumb, and these thumb-like toes turn the one set to the right, and the other to the left. The AmericanCheirotheriumwas evidently a broader animal, and belonged to a distinct genus from that of the triassic age in Europe.[338-A]
Fig. 386.Scale one-sixth the original.Slab of sandstone from the coal-measures of Pennsylvania, with footprints of air-breathing reptile and casts of cracks.
Fig. 386.
Scale one-sixth the original.Slab of sandstone from the coal-measures of Pennsylvania, with footprints of air-breathing reptile and casts of cracks.
We may assume that the reptile which left these prints on theancient sands of the coal-measures was an air-breather, because its weight would not have been sufficient under water to have made impressions so deep and distinct. The same conclusion is also borne out by the casts of the cracks above described, for they show that the clay had been exposed to the air and sun, so as to have dried and shrunk.
Fig. 387.Series of reptilian footprints in the coal-strata of Westmoreland County, Pennsylvania.a.Mark of nail?
Fig. 387.
Series of reptilian footprints in the coal-strata of Westmoreland County, Pennsylvania.
a.Mark of nail?
The geological position of the sandstone of Greensburg is perfectly clear, being situated in the midst of the Appalachian coal-field,having the main bed of coal, called the Pittsburg seam, above mentioned (p. 331.), 3 yards thick, 100 feet above it, and worked in the neighbourhood, with several other seams of coal at lower levels. The impressions ofLepidodendron,Sigillaria,Stigmaria, and other characteristic carboniferous plants, are found both above and below the level of the reptilian footsteps.
Analogous footprints of a large reptile of still older date have since been found (1849), by Mr. Isaac Lea, in the lowest beds of the coal formation at Pottsville, near Philadelphia, so that we may now be said to have the footmarks of two reptilians of the coal period, and the skeletons of four.[340-A]
We have already seen that this rock lies sometimes entirely beneath the coal-measures, while, in other districts, it alternates with the shales and sandstone of the coal. In both cases it is destitute of land plants, and usually charged with corals, which are often of large size; and several species belong to the lamelliferous class of Lamarck, which enter largely into the structure of coral reefs now growing. There are also a great number ofCrinoidea(seefig. 388.), and a fewEchinoderms, associated with the zoophytes above mentioned. TheBrachiopodaconstitute a large proportion of the Mollusca, many species being referable to two extinct genera,Spirifer(orSpirifera) (fig. 389.), andProductus(Leptæna) (fig. 390.).
Fig. 388.Cyathocrinites planus,Miller. Mountainlimestone.
Fig. 388.
Cyathocrinites planus,Miller. Mountainlimestone.
Fig. 389.Spirifer glaber, Sow. Mountain limestone.
Fig. 389.
Spirifer glaber, Sow. Mountain limestone.
Fig. 390.Productus Martini, Sow. (P. semireticulatus, Flem.) Mountain limestone.
Fig. 390.
Productus Martini, Sow. (P. semireticulatus, Flem.) Mountain limestone.
Among the spiral univalve shells the extinct genusEuomphalus(seefig. 391.) is one of the commonest fossils of the Mountain limestone. In the interior it is often divided into chambers (seefig. 391.d); the septa or partitions not being perforated, as in foraminiferous shells, or in those having siphuncles, like the Nautilus. The animal appears, like the recentBulimus decollatus, to have retreated at different periods ofits growth, from the internal cavity previously formed, and to have closed all communication with it by a septum. The number of chambers is irregular, and they are generally wanting in the innermost whorl.
Fig. 391.Euomphalus pentagulatus, Min.Con. Mountainlimestone.a.Upper side;b.lower, or umbilical side;c.view showing mouth which is less pentagonal in older individuals;d.view of polished section, showing internal chambers.
Fig. 391.
Euomphalus pentagulatus, Min.Con. Mountainlimestone.
a.Upper side;b.lower, or umbilical side;c.view showing mouth which is less pentagonal in older individuals;d.view of polished section, showing internal chambers.
Fig. 392.Portion ofOrthoceras laterale,Phillips. Mountainlimestone.
Fig. 392.
Portion ofOrthoceras laterale,Phillips. Mountainlimestone.
There are also many univalve and bivalve shells of existing genera in the Mountain limestone, such asTurritella,Buccinum,Patella,Isocardia,Nucula, andPecten.[341-A]But theCephalopodadepart, in general, more widely from living forms, some being generically distinct from all those found in strata newer than the coal. In this number may be mentionedOrthoceras, a siphuncled and chambered shell, like aNautilusuncoiled and straightened. Some species of this genus are several feet long (fig. 392.). TheGoniatiteis another genus, nearly allied to theAmmonite, from which it differs in having the lobes of the septa free from lateral denticulations, or crenatures; so that the outline of these is continuous and uninterrupted (seea,fig. 393.). Their siphon is small, and in the form of the striæ of growth they resembleNautili. Another extinct generic form ofCephalopod, abounding in the Mountain limestone, and not found in strata of later date, is theBellerophon(fig. 394.), of which the shell, like the living Argonaut, was without chambers.
Fig. 393.Goniatites evolutus, Phillips.[342-A]Mountain limestone.
Fig. 393.
Goniatites evolutus, Phillips.[342-A]Mountain limestone.
Fig. 394.Bellerophon costatus, Sow.[342-B]Mountain limestone.
Fig. 394.
Bellerophon costatus, Sow.[342-B]Mountain limestone.
Old Red Sandstone of Scotland, and borders of Wales — Fossils usually rare — "Old Red" in Forfarshire — Ichthyolites of Caithness — Distinct lithological type of Old Red in Devon and Cornwall — Term "Devonian" — Organic remains of intermediate character between those of the Carboniferous and Silurian systems — Corals and shells — Devonian strata of Westphalia, the Eifel, Russia, and the United States — Coral reef at Falls of the Ohio — Devonian flora.
Old Red Sandstone of Scotland, and borders of Wales — Fossils usually rare — "Old Red" in Forfarshire — Ichthyolites of Caithness — Distinct lithological type of Old Red in Devon and Cornwall — Term "Devonian" — Organic remains of intermediate character between those of the Carboniferous and Silurian systems — Corals and shells — Devonian strata of Westphalia, the Eifel, Russia, and the United States — Coral reef at Falls of the Ohio — Devonian flora.
Itwas stated in Chap. XXII. that the Carboniferous formation is surmounted by one called the "New Red," and underlaid by another called the "Old Red Sandstone."[342-C]The British strata of the last mentioned series were first recognized in Herefordshire and Scotland as of great thickness, and immediately subjacent to the coal; but they were in general so barren of organic remains, that it was difficult to find paleontological characters of sufficient importance to distinguish them as an independent group. In Scotland, and on the borders of Wales, the "Old Red" consists chiefly of red sandstone, conglomerate, and shale, with few fossils; but limestones of the same age, peculiarly rich in organic remains, were at length found in Devonshire.
I shall first advert to the characters of the group as developed in Herefordshire, Worcestershire, Shropshire, and South Wales. Its thickness has been estimated at 8000 feet, and it has been subdivided into—
1st. A quartzose conglomerate passing downwards into chocolate-red and green sandstone and marl.
2d. Cornstone and marl—red and green argillaceous spotted marls, with irregular courses of impure concretionary limestone, provincially called Cornstone.
Here, as usual, fossils are extremely rare in the clays and sandstones in which the red oxide of iron prevails; but remains of fishes of the generaCephalaspisandOnchushave been discovered in the Cornstone.
The whole of the northern part of Scotland, from Cape Wrath to the southern flank of the Grampians, has been well described by Mr. Miller as consisting of a nucleus of granite, gneiss, and other hypogene rocks, which seem as if set in a sandstone frame.[343-A]The beds of the Old Red Sandstone constituting this frame, may once perhaps have extended continuously over the entire Grampians before the upheaval of that mountain range; for one band of the sandstone follows the course of the Moray Frith far into the interior of the great Caledonian valley; and detached hills and island-like patches occur in several parts of the interior, capping some of the higher summits in Sutherlandshire, and appearing in Morayshire like oases among the granite rocks of Strathspey. On the western coast of Ross-shire, the Old Red forms those three immense insulated hills before described (p. 67.), where beds of horizontal sandstone, 3000 feet high, rest unconformably on a base of gneiss, attesting the vast denudation which has taken place.
But in order to observe the uppermost part of the Old Red, we must travel south of the Grampians, and examine its junction with the bottom of the Carboniferous series in Fifeshire. This upper member may be seen in Dura Den, south of Cupar, to consist of a belt of yellow sandstone, in which Dr. Fleming first discovered scales ofHoloptychius, and in which species of fish of the generaPterichthys,Pamphractus, and others, have been met with. (For genusPterichthys, seefig. 400.p. 345.)
The beds next below the yellow sandstone are well seen in the large zone of Old Red which skirts the southern flank of the Grampians from Stonehaven to the Frith of Clyde. It there forms, together with trap, the Sidlaw Hills and the strata of the valley of Strathmore. A section of this region has been already given (p. 48.), extending from the foot of the Grampians in Forfarshire to the sea at Arbroath, a distance of about 20 miles, where the entire series of strata is several thousand feet thick, and may be divided into three principal masses: 1st, and uppermost, red and mottled marls, cornstone, and sandstone (Nos. 1. and 2. of the section); 2d, Conglomerate, often of vast thickness (No. 3. ibid.); 3d, Roofing and paving stone, highly micaceous, and containing a slight admixture of carbonate of lime (No. 4. ibid.). In the first of these divisions, which may be considered as succeeding the yellow sandstone of Fifeshire before mentioned, a gigantic species of fish of the genusHoloptychiushas been found at Clashbinnie near Perth. Some scales (seefig. 395.) have been seen which measured 3 inches in length by 21/2in breadth.
At the top of the next division, or immediately under the conglomerate(No. 3.p. 48.), there have been found in Forfarshire some remarkable crustaceans, with several fish of the genus named by AgassizCephalaspis, or "buckler-headed," from the extraordinary shield which covers the head (seefig. 396.), and which has often been mistaken for that of a trilobite, of the divisionAsaphus.
Fig. 395.Scale ofHoloptychius nobilissimus, Agas. Clashbinnie. Nat. size.
Fig. 395.
Scale ofHoloptychius nobilissimus, Agas. Clashbinnie. Nat. size.
Species of the same genus are considered in England as characteristic of the second or Cornstone division (p. 343.).
Fig. 396.Cephalaspis Lyellii,Agass. Length63/4inches. From a specimen in my collection found at Glammiss, in Forfarshire. See other figures, Agassiz, vol. ii. tab. 1.a. and 1.b.a.One of the peculiar scales with which the head is covered when perfect. These scales are generally removed, as in the specimen above figured.b, c.Scales from different parts of the body and tail.
Fig. 396.
Cephalaspis Lyellii,Agass. Length63/4inches. From a specimen in my collection found at Glammiss, in Forfarshire. See other figures, Agassiz, vol. ii. tab. 1.a. and 1.b.
Fig. 397.Eggs of gasteropodous mollusk?Lower beds of Old Red, Ley's Mill, Forfarshire.
Fig. 397.
Eggs of gasteropodous mollusk?Lower beds of Old Red, Ley's Mill, Forfarshire.
Fig. 398.Fucoids and eggs of gasteropodous mollusk?Lower Old Red, Fife.
Fig. 398.
Fucoids and eggs of gasteropodous mollusk?Lower Old Red, Fife.
In the same grey paving-stones and coarse roofing-slates, in which theCephalaspisoccurs, in Forfarshire and Kincardineshire, the remains of marine plants or fucoids abound. They are frequently accompanied by groups of hexagonal, or nearly hexagonal markings, which consist of small flattened carbonaceous bodies, placed in a slight depression of the sandstone or shale. (Seefigs. 397and398.) They much resemble in form the spawn of the recent Natica (seefig. 399.), in which the eggs are arranged in a thin layer of sand, and seem to have acquired a polygonal form by pressing against each other. The substance of the egg, if fossilized, might give rise to small pellicles of carbonaceous matter.
Fig. 399.Fragment of spawn of British species ofNatica.
Fig. 399.
Fragment of spawn of British species ofNatica.
These fossils I have met with, both to the north of Strathmore, in the vertical shale beneath the conglomerate, and in the same beds in the Sidlaw hills, at all the points wherefig. 4.is introduced in the section,p. 48.
Fig. 400.Pterichthys, Agassiz; upper side, showing mouth; as restored by H. Miller.[345-A]
Fig. 400.
Pterichthys, Agassiz; upper side, showing mouth; as restored by H. Miller.[345-A]
Beds of red shale and red sandstone, sometimes associated with pudding-stone (older than No. 3.,fig. 62.p. 48.), and destitute of organic remains, separate, in the region of Strathmore, the above-described fossiliferous strata from the older crystalline rocks of the Grampians. But, in the north of Scotland, we find, at the base of the Old Red, other grey slaty sandstones, in the counties of Banff, Nairn, Moray, Cromarty, Caithness, and in Orkney, rich in ichthyolites of peculiar forms, belonging to the generaPterichthys(fig. 400.),Coccosteus,Diplopterus,Dipterus,Cheiracanthus, and others of Agassiz.
Five species ofPterichthyshave been found in this lowest division of the Old Red. The wing-like appendages, whence the genus is named, were first supposed by Mr. Miller to be paddles, like those of the turtle; but Agassiz regards them as weapons of defence, like the occipital spines of the River Bull-head (Cottus gobio, Linn.); and considers the tail to have been the only organ of motion. The generaDipterusandDiplopterusare so named, because their two dorsal fins are so placed as to front the anal and ventral fins, so as to appear like two pairs of wings. They have bony enamelled scales.
South Devon and Cornwall.—A great step was made in the classification of the slaty and calciferous strata of South Devon and Cornwall in 1837, when a large portion of the beds, previously referred to the "transition" or most ancient fossiliferous series, were found to belong in reality to the period of the Old Red Sandstone. For this reform we are indebted to the labours of Professor Sedgwick and Sir R. Murchison, assisted by a suggestion of Mr. Lonsdale, who, in 1837, after examining the South Devonshire fossils, perceived that some of them agreed with those of the Carboniferous group, others with those of the Silurian, while many could not be assigned to eithersystem, the whole taken together exhibiting a peculiar and intermediate character. But these paleontological observations alone would not have enabled us to assign, with accuracy, the true place in the geological series of these slate-rocks and limestones of South Devon, had not Messrs. Sedgwick and Murchison, in 1836 and 1837, discovered that the culmiferous or anthracitic shales of North Devon belonged to the Coal, and not, as preceding observers had imagined, to the transition period.
As the strata of South Devon here alluded to are far richer in organic remains than the red sandstones of contemporaneous date in Herefordshire and Scotland, the new name of the "Devonian system" was proposed as a substitute for that of Old Red Sandstone.
The rocks of this group in South Devon consist, in great part, of green chloritic slates, alternating with hard quartzose slates and sandstones. Here and there calcareous slates are interstratified with blue crystalline limestone, and in some divisions conglomerates, passing into red sandstone.
The link supplied by the whole assemblage of imbedded fossils, connecting as it does the paleontology of the Silurian and Carboniferous groups, is one of the highest interest, and equally striking, whether we regard thegeneraof corals or of shells. Thespeciesare almost all distinct.
Among the more abundant corals, we find the generaFavositesandCyathophyllum, common on the one hand to the Mountain limestone, and on the other to the Silurian system. Some few even of thespeciesare common to the Devonian and Silurian groups, as, for example,Favosites polymorpha(fig. 401.), very abundant in South Devon.
Fig. 401.Favosites polymorpha, Goldf., S.Devon. Froma polished specimen.a.portion of the same, magnified to show the pores.
Fig. 401.
Favosites polymorpha, Goldf., S.Devon. Froma polished specimen.
a.portion of the same, magnified to show the pores.
TheCyathophyllum cæspitosum(fig. 402.) andPorites pyriformis(fig. 424.p. 356.) are more peculiarly characteristic of the Devonian rocks.
In regard to the shells, all the brachiopodous genera, such asTerebratula,Orthis,Spirifer,Atrypa, andProductus, which are found in the Mountain limestone, occur, together with those of the Silurian system, except thePentamerus. Some forms, however, seem exclusively Devonian, as for example,Calceola sandalina(fig. 403.) andStrygocephalus Burtini(fig. 404.), which have been met with both in the Eifel, in Germany, and in Devonshire, in the very lowest Devonian beds.
Fig. 402.a.Cyathophyllum cæspitosum, Goldf., Plymouth.b.a terminal star.c.vertical section exhibiting transverse plates, and part of another branch.
Fig. 402.
Among the peculiar lamellibranchiate bivalves, also common to Devonshire and the Eifel, we findMegalodon cucullatus(fig. 405.). Several spiral univalves are abundant, among which are many species ofPleurotomariaandEuomphalus. Among the Cephalopoda we findBellerophonandOrthoceras, as in the Silurian and Carboniferous groups, andGoniatiteandCyrtoceras, as in the Carboniferous. In some of the upper Devonian beds, a shell, resembling a flattenedGoniatite, occurs, calledClymenia, by Munster (Endosiphonites, Ansted.[347-A]).
Fig. 403.Calceola sandalina,Lam. Eifel;also South Devon.a.both valves united.b.inner side of opercular valve.
Fig. 403.
Calceola sandalina,Lam. Eifel;also South Devon.
Fig. 404.Strygocephalus Burtini. (Terebratula porrecta,Sow.) Eifel;also South Devon.a.valves united.b. side view of same.c.interior of larger valve, showing thick partition, and thinner one continued from it.
Fig. 404.
Strygocephalus Burtini. (Terebratula porrecta,Sow.) Eifel;also South Devon.
Fig. 405.Megalodon cucullatus,Sow. Eifel;also Bradley, S. Devon.a.the valves united.b.interior of valve, showing the large cardinal tooth.
Fig. 405.
Megalodon cucullatus,Sow. Eifel;also Bradley, S. Devon.
Fig. 406.Clymenia linearis,Munster. (Endosiphonites carinatus,Ansted.) Cornwall.
Fig. 406.
Clymenia linearis,Munster. (Endosiphonites carinatus,Ansted.) Cornwall.
A peculiar species of trilobite, calledBrontes flabellifer(fig. 407.), is found in the Devonian strata of the Eifel and in South Devon. It should be observed, however, that the head in the specimen here figured by Goldfuss, the most perfect which could be obtained, is incomplete, and a restoration has been attempted by Mr. Salter infig. 408., from data supplied by other species of the same genus occurring in older rocks.
Fig. 407.Brontes flabellifer, Goldf. Eifel; also S. Devon.
Fig. 407.
Brontes flabellifer, Goldf. Eifel; also S. Devon.
Fig. 408.Restored outline of head ofBrontes flabellifer.
Fig. 408.
Restored outline of head ofBrontes flabellifer.
For determining the true equivalents of the Devonian group in the Rhenish provinces and adjacent parts of Germany, we are indebted to the labours of Messrs. Sedgwick and Murchison, in 1839, from which it appears that rocks of that age emerge from beneath the coal-field of Westphalia, and are also found in troughs among the Silurian rocks in Nassau. Many of the limestones, particularly those on the river Lahn, are identical, both in structure and in coralline remains, with the beautiful marbles of Babbacombe, Torquay, and Plymouth.
The limestones of the Eifel, long ago celebrated for their fossils, and which lie in a basin supported by Silurian rocks, are found to be referable to the lower part of the Devonian system.
In Russia, also, Messrs. Murchison and De Verneuil have shown (1840) that the "Old Red" group occupies a wide area south from St. Petersburg. It was formerly supposed to be the New Red Sandstone, on account of its saliferous and gypseous beds; but it isnow proved to be the Old Red by containing ichthyolites of genera which characterize this group in the British Isles, as, for example,Holoptychius,Coccosteus,Diplopterus, &c.[349-A], associated with mollusca found in the Devonian of Western Europe. Among the fish are also many species of sharks of the Cestraciont division, a fact worthy of notice, because the squaloid fishes of the present day offer the highest organization of the brain and of the generative organs, and make, in these respects, the nearest approach to the higher vertebrate classes.
The position of this formation between the carboniferous rocks of Pennsylvania and Ohio, is pointed out in the section,fig. 379.p. 327., and it is a remark of M. de Verneuil that in no European country is there so complete and uninterrupted a development of the Devonian system as in North America. At the falls of the Ohio, at Louisville, in Kentucky, there is a grand display of one of the limestones of this period, resembling a modern coral reef. A wide extent of surface is exposed in a series of horizontal ledges, at all seasons, when the water is not high; and the softer parts of the stone having decomposed and wasted away, the harder calcareous corals stand out in relief, and many of them send out branches from their erect stems precisely as if they were living. Among other species I observed large masses, not less than 5 feet in diameter, ofFavosites gothlandica, with its beautiful honeycomb structure well displayed, and, by the side of it, theFavistella, combining a similar honeycombed form with the star of theAstrea. There was also the cup-shapedCyathophyllum, and the delicate network of theFenestella, and that elegant and well-known European species of fossil, called "the chain coral,"Catenipora escharoides, with a profusion of others (seefig. 423.p. 355.). These coralline forms were mingled with the joints, stems, and occasionally the heads, of lily encrinites. Although hundreds of fine specimens have been detached from these rocks, to enrich the museums of Europe and America, another crop is constantly working its way out, under the action of the stream, and of the sun and rain, in the warm season when the channel is laid dry. The waters of the Ohio, when I visited the spot in April, 1846, were more than 40 feet below their highest level, and 20 feet above their lowest, so that large spaces of bare rock were exposed to view.[349-B]
With the exception of the fucoids above mentioned (p. 344.), but little is known with certainty of the plants of the Devonian group. Those found in the department of La Sarthe in France, and in various parts of Brittany, formerly referred to the Devonian era, have beenshown (in 1850), by M. de Verneuil, to belong to the carboniferous series. The same may be said of the species ofLepidodendron,Knorria,Calamite,Sagenaria, and other genera recently figured (1850), by Mr. F. A. Römer, from the formation called "Greywacké à Posodonomyes" in the Hartz.[350-A]They are accompanied byGoniatites reticulatusPhillips,G. intercostatusPhil., and other mountain limestone species, and had been previously assigned to the oldest part of the carboniferous series by Messrs. Murchison and Sedgwick.
If hereafter we should become well acquainted with the land plants of the Devonian era, we may confidently expect that nearly all of them will agree generically with those of the carboniferous period, but the species will be as different as are the Devonian vertebrate and invertebrate animals from the fossil species of the Coal.
Silurian strata formerly called transition — Term grauwacké — Subdivisions of Upper and Lower Silurian — Ludlow formation and fossils — Wenlock formation, corals and shells — Caradoc and Llandeilo beds — Graptolites — Lingula — Trilobites — Cystideæ — Vast thickness of Silurian strata in North Wales — Unconformability of Caradoc sandstone — Silurian strata of the United States — Amount of specific agreement of fossils with those of Europe — Great number of brachiopods — Deep-sea origin of Silurian strata — Absence of fluviatile formations — Mineral character of the most ancient fossiliferous rocks.
Silurian strata formerly called transition — Term grauwacké — Subdivisions of Upper and Lower Silurian — Ludlow formation and fossils — Wenlock formation, corals and shells — Caradoc and Llandeilo beds — Graptolites — Lingula — Trilobites — Cystideæ — Vast thickness of Silurian strata in North Wales — Unconformability of Caradoc sandstone — Silurian strata of the United States — Amount of specific agreement of fossils with those of Europe — Great number of brachiopods — Deep-sea origin of Silurian strata — Absence of fluviatile formations — Mineral character of the most ancient fossiliferous rocks.
Wecome next in the descending order to the most ancient of the primary fossiliferous rocks, that series which comprises the greater part of the strata formerly called "transition" by Werner, for reasons explained in Chap. VIII., pp.91and92.Geologists have also applied to these older strata the general name of "grauwacké," by which the German miners designate a particular variety of sandstone, usually an aggregate of small fragments of quartz, flinty slate (or Lydian stone), and clay-slate cemented together by argillaceous matter. Far too much importance has been attached to this kind of rock, as if it belonged to a certain epoch in the earth's history, whereas a similar sandstone or grit is found sometimes in the Old Red, and in the Millstone Grit of the Coal, and sometimes in certain Cretaceous and even Eocene formations in the Alps.
The name ofSilurianwas first proposed by Sir Roderick Murchison, for a series of fossiliferous strata lying below the Old Red Sandstone, and occupying that part of Wales and some contiguous counties of England, which once constituted the kingdom of theSilures, a tribe of ancient Britons. The strata have been dividedinto Upper and Lower Silurian, and these again in the region alluded to admit of several well-marked subdivisions, all of them explained in the following table.
Ludlow formation.—This member of the Upper Silurian group, as will be seen by the above table, is of great thickness, and subdivided into four parts,—the Tilestone, the Upper and Lower Ludlow, and the intervening Aymestry limestone. Each of these may be distinguished near the town of Ludlow, and at other places in Shropshire and Herefordshire, by peculiar organic remains.
1.Tilestones.—This uppermost division was originally classed by Sir R. Murchison with the Old Red Sandstone, because they decompose into a red soil throughout the Silurian region. At the same time he regarded the tilestones as a transition group forming a passage from Silurian to Old Red. It is now ascertained that the fossils agree in great part specifically, and in general character entirely, with those of the succeeding formation.
2.Upper Ludlow.—The next division, called the Upper Ludlow, consists of grey calcareous sandstone, decomposing into soft mud, and contains, among other shells, theLingula cornea, which is common to it and the lowest, or tilestone beds of the Old Red. ButtheOrthis orbicularisis peculiar to the Upper Ludlow, and very common; and the lowest or mudstone beds, are loaded for a thickness of 30 feet withTerebratula navicula(fig. 410.), in vast numbers. Among the cephalopodous mollusca occur the generaBellerophonandOrthoceras, and among the crustacea theHomalonotus(fig. 418.p. 354.). A coral calledFavosites polymorpha, Goldf. (fig. 401.p. 346.) is found both in this subdivision and in the Devonian system.