APPENDIX.
APPENDIX.
METEOROLOGICAL REGISTER.MORZOUK.
We set out at this time on our journey to the south; for account of Thermometer see Journal.
I heresubjoin a short account, by Professor Buckland of Oxford, of a few specimens of the rocks and minerals of Tripoli and Fezzan, which I was enabled to collect in the course of my tour.
It appears to Mr. Buckland, from these specimens, that the kingdoms of Tripoli and Fezzan present, in their geological structure, a striking resemblance to the rocks of Europe; and are composed of strata, which are distinctly referrible to the three following formations:
1.Basalt.2.Tertiary Limestone, of nearly the same age with the Calcaire Grossier of Paris.3.New Red Sand Stone.
1. The Basaltic Rocks appear to constitute the great chain of the Soudah or Black Mountains, near the northern extremity of the kingdom of Fezzan, not far from Sockna; they extend in breadth nearly 100 miles from north to south, and run as far as the eye can reach from east to west.
2. The Tertiary Limestone, or Calcaire Grossier, containing marine shells in a state of delicate preservation, is found in Tripoli, on the two opposite edges of the desert that lies between the town of Benioleed and castle of Bonjem, and appears to be of the same age and formation with depositions of a similar kind that occur in Malta and Sicily, and on the north side of the Mediterranean, on the coasts of Italy and France.
3. The New Red Sand Stone formation appears under its usual form of loose red sand, accompanied by salt and gypsum, andassociated with beds of a calcareous breccia, cemented by magnesian limestone, and with beds of compact dolomite.
There are no primitive rocks, and one specimen only which seems referrible to a granular quartz rock, more ancient than the new red sand stone.
A short descriptive catalogue of the specimens which have been brought home, with the assistance of the map in which all the names alluded to are inserted, will give the most ready information they are calculated to afford.
The specimens are as follow:
basalt.
No. 1. Basalt, nearly black, much impregnated throughout with carbonate of lime, and interspersed with small circular cells, that are partly or wholly filled with common or with magnesian carbonate of lime. The decomposition of this rock forms small spherical fragments of considerable hardness, the surface of which, by long exposure, has acquired a kind of polish or glossy aspect, and is irregularly pitted or indented all over with small cavities of various depths, from the destruction of the calcarous matter that originally filled them.
A similar appearance of glossy polish is found on all the calcareous specimens from this country, which appear to have been long exposed to the action of the atmosphere. In some of these the surface is entirely smooth and even; in others, it is furrowed over with minute grooves and channels, intersecting each other with irregular curvatures, and resembling the appearance produced on the surface of compact limestone that has been submitted to the action of acids, or corroded by small marine worms.
It is not easy to determine the cause of this irregular destruction of the surface of limestone, whose substance appears to be entirely uniform: it is probably the same that gives it the glossy polish; but it seems doubtful, whether the agent producing it be the continualdrifting of fine siliceous sand, or the action of the atmosphere under exposure to a burning sun. A similar gloss appears on the surface of many fragments of flint and compact siliceous limestone that have been long exposed on the surface of the soil, on the summit of Martre near Paris; and in this case, I think, it can only be referred to the action of the sun and atmosphere.
The chain of the Soudah or Black Mountains appears to be composed of this basalt; they rise to an elevation of about 1500 feet, being situated at a short distance on the south from Sockna, and extending about 100 miles in breadth from north to south, and in length as far as the eye can reach, from east to west; they are perfectly barren, of irregular form, occasionally broken into detached masses, and sometimes rising into cones. Their elevated plains are in some parts covered with the small spherical shining fragments above described. The latitude of this chain is from 28·40. to 27·30. north. Traces of basalt occur also near Tripoli, in lat. 32. at a spot called Black Dog, on the north of Beneabbas, and in a valley through which the road passes from Beneabbas to Benioleed.
2. An unrolled agate from Om el a Beed, near Zeghen, on the south of the Black Mountains. The occurrence of fragments of basalt, in this same neighbourhood, renders it probable that basaltic rocks exist in Situ, near the Pass of Kenair.
tertiary formations.
3. Two species of cardium, in a state of delicate preservation, resembling that of the shells of Grignon, near Paris, and embedded in a loose white sand, which has the appearance and degree of adhesion of coarse white sugar, from a gravelly plain on the north of Bonjem.
4. Slightly crystalline limestone, of a dark yellow colour, and loaded with fragments of organic remains, amongst which the most distinct are referrible to the genus Ostrea and Pecton. It is found in a mountain of Tripoli, thirty miles south of Benioleed. Thislimestone appears to be nearly of the same era with the Calcaire Grossier of Paris, and is separated only by a large desert plain from the deposit of shells last mentioned at Bonjem. The probable connexion of these strata with the tertiary formations in other adjacent parts on the coast of the Mediterranean, has been already suggested.
5. Soft, highly calcareous marl stone, of a light mottled gray colour, resembling in appearance the chalk marl of England: it is said occasionally to be streaked with red, and to contain modules of flint. It occurs in the Mountains of Mejdool, in lat. 26.
6. Quartzose sand dispersed through a matrix of indurated green clay, and affording the materials of which the town of Traghan is built.
It is probable that these two last specimens, 5 and 6, are from strata not more ancient than the chalk of England, and possibly connected with the tertiary formations, No. 3 and 4.
new red sand stone.
7. Sand collected fifty miles on the north of Sockna, during a gale of wind from the drift sand, which is blown about the desert. It is composed of extremely minute grains of red semi-transparent quartz; observed with a lens, these grains appear to be rounded fragments, and present no crystalline facets. They possess, in a strong degree, that peculiar tint of red, which has caused the name of red sand stone to be applied to certain extensive formations which it pervades in Europe.
The frequent occurrence of salt springs, and of rock salt and gypsum in the deserts of Africa, goes far to identify the sand of this continent with the new red sand in the south of England, which is characterised by containing similar mineral substances. It is still farther allied to it in being accompanied by strata of calcareous breccia and beds of limestone; in all of which magnesia is a considerable ingredient.
8, 9, 10. Ferruginous concretions, forming aetites or geodes in the red sand shore. The broken fragments are compact, sonorous, and of a dark liver colour, having a shining polished surface. The sand which formed their matrix still adheres to the exterior of some of them. They occur on a plain and a mountain near Om el a Beed. In lat. 27°⁵⁄₁₀: they are here so abundant, as almost entirely to cover the ground, and impart to it a dark red colour. This accumulation of them probably arises from the wind having drifted away the fine sand, in which they were formed, leaving behind the heavy bodies in question.
A little farther north, at the foot of the Pass of Kenair, near some steep sand hills, is a narrow bed almost entirely composed of tubular concretions of iron of similar origin, irregularly ramifying through the sand like roots of trees, and producing a rugged appearance, which at first sight resembles a bed of lava.
11. Flat lamina of variegated sand stone, held together by a calcareous cement, and covered on each side by small spherical tubercles closely studded by the side of each other. Similar concretions are common in the imperfect beds of sand stone strata of all formations.
12. Flesh-coloured marl, full of small irregular crystals of selenite. The colour of this marl resembles that of the rock marl of England: it is from a plain near Gatrone, lat. 25°.
13. Fibrous gypsum passing into foliated, apparently from a matrix of ochreous marl stone.
14. Crystals of calcareous spar imbedded in yellow-ochre. Found with No. 13, in the same mountain with the Calcaire Grossier, No. 4, thirty miles south of Benioleed.
15 and 16. Fibrous and foliated gypsum from a similar matrix of ochreous marl to No. 13 and 14, and found on the same plain, near Bonjem, with the two species of cardium, No. 3.
It is probable these last four specimens come from a stratummore nearly allied to the gypsum formation of Paris than to the red marl to which I have referred the other specimen of gypsum, No. 12.
magnesian limestone, or dolomite.
17. Limestone, very compact, and strongly impregnated with magnesia, and is of a yellowish white colour; occurs split into small laminated fragments, like broken tiles. The ground is covered with these fragments, which break and rattle under the feet like pottery. It is found in the plain between Zuela and Omesoguin, lat. 26°.
18 and 19. From the plain that lies between the Black Mountains and Pass of Kenair. Both these specimens are compact limestone, of a dark flesh colour, and contain much magnesia. This plain is covered with small shining fragments of this limestone, particularly near El Gaaf; and their exposed surfaces are corroded and furrowed over with the small irregular grooves and channels already mentioned in the note to No. 1.
20. Flesh-coloured dolomite, mottled with yellow. From the north base of the Black Mountains.
21. Hard compact dolomite, of an ochre yellow colour. From the Well of Gutfa, between the north base of the Black Mountains and town of Sockna.
22 and 23. Brecciated dolomite, of yellowish white colour, full of knobs and concretions of the same. Found on the plain near Sockna.
24 and 25. Brecciated dolomite, of dark flesh colour, full of small angular concretions of the same substance, but in more compact state than that which forms the cement by which they are held together. These are found near the compact flesh-coloured dolomite, No. 18 and 19, in the plain of El Gaaf.
All the above specimens, from 17 to 25, are much impregnatedwith magnesia, and distinctly referrible to similar strata that form subordinate beds in the new red sand-stone formation of England; and they seem to occupy a similar position in the red sand-stone of the desert plains that lie on the north and south side of the basaltic chain of the Black Mountains in Fezzan.
26. A pudding-stone, composed of pebbles of dolomite, united by a granulated calcareous cement. Taken from a Roman castle at Bonjem. The surface of this specimen has the same glossy polish which has been before mentioned in some others.
27. Specimen of the materials of which the Castle of Zuela and many other old castles are constructed. It is an artificial compound, made up of small grains of quartz of the size of millet seed, imbedded in a cement or paste of yellowish marl, which effervesces rapidly with acids: there is no more marl than is sufficient to hold together the grains of quartz. Buildings are constructed of this material by pressing the composition into cases, which are removed when it is dry.
28. Milk-white compact carbonate of lime. From the plain between the Black Mountains and Pass of Kenair. It is beautifully furrowed over with small channels and grooves, like No. 18 and 19.
29. White limestone, of coarser grain. From ditto.
30. White limestone, filled with grains of fine white quartz. From ditto.
31. White limestone. From the north base of the Black Mountains.
32. Compact yellow carbonate of lime, having a polished glossy surface, beautifully furrowed, and resembling a bit of yellow bees’ wax. From the north base of the Black Mountains.
These last specimens of carbonate of lime are found with those of dolomite described immediately before, and seem to belong to the same formation with them.
It appears then, as far as can be collected from the few specimens above described, that on each side of the central basaltic chain of the Soudah or Black Mountains, the plains of the desert are composed of red sand and sand-stone, containing gypsum and rock salt, and associated with beds of dolomite and common carbonate of lime. All these characters identify most distinctly the sand of the desert of Africa with the new red sand-stone of England. There are no specimens which indicate the existence of any other formations on the south side of the Black Mountains from lat. 29° to 24°, except the marl-stone and green clay (No. 5 and 6); which lead us to suspect strata of tertiary formation in lat. 26°, near Mejdool, on the east of Morzouk. At the north base of the central chain, strata belonging to the same red sand-stone formation seem to extend nearly to Bonjem on the frontiers of Fezzan and Tripoli; where the basis formations appear, and probably repose on them in irregular patches in the desert that divides this place from the mountains on the north of the town of Tripoli. These mountains extend east and west nearly parallel to the coast of the Mediterranean, from long. 15° to 13°; but as no specimens have been brought home from them, it is impossible to do more than conjecture to what formation they belong: from notices inserted in the map, they appear to contain trap and calcareous rocks. The nearest point from which we have a specimen is Benioleed (No. 4): and this is probably referrible to the calcaire grossier of Paris.
One solitary specimen from the eastern extremity of these calcareous mountains possesses no character sufficiently distinct to show whether it be calcaire grossier or jura limestone. It seems, however, to belong to one of these two formations.
The only specimen remaining to be described is No. 34; a yellow quartzose sand-stone, having a glassy fracture, and in some of its component grains having a sapphire blue colour. It resemblesthe sandstone of which is composed the statue of the Old Memnon in Egypt; and was found near the north base of the Black Mountains. As it is not a rolled pebble, it indicates, that in addition to basalt there are strata of ancient quartzose sandstone in this chain, which forms nearly the centre of the line along which the specimens above described have been collected.