Imágenes de páginas
PDF
EPUB

the subject with a few cursory generalities, have rather induced us to collect with the utmost care all the materials we could procure. These, indeed, are few, for of older authorities we believe there are none; and this remark includes, as already hinted, the learned Forskal, whose researches do not embrace those countries. It is true that the eminent Danish naturalist supplied a DESCRIPTION OF ANIMALS in his Oriental Itinerary, as also a FLORA of Egypt and Arabia;† but Oriental is a wide word, and Forskal laboured chiefly in the neighbourhood of Alexandrea; while the Arabia he examined was not the vast plains of the Petræa and Deserta which border upon Mesopotamia, but a small portion of the promontory of Arabia Felix, near Mocha; and both these districts are distant not less than a thousand miles from the regions which now engage our attention. Hence, though we do not mean to deny that some useful analogies in botany and zoology may be drawn from his works, yet all inferences of this nature must be deduced with the greatest caution. Under these circumstances, we must have recourse to such notices as can be procured from modern travellers, few of whom are professed naturalists. A distinguished exception, however, occurs in the case of the recent expedition to the Euphrates, under the charge of Colonel Chesney. Without the documents published in connexion with this survey, and especially the Researches of Mr. Ainsworth, so often already alluded to, we could not have supplied any notice whatever on this interesting subject. From that publication we have drawn with the utmost freedom; and beg now, once for all, to acknowledge our obligation to the labours and authority of the enlightened author. At the same time, we have not neglected whatever other sources of information we could discover; and hence we presume to hope that the following description will not be found devoid either of interest or instruction.

* Descriptiones Animalium quæ in Itinere Orientali observavit Petrus Forskal. Hauniæ, 1775.

† Flora Ægyptiaco-Arabica, sive Descriptiones Plantarum quas per Ægyptum Inferiorem et Arabiam Felicem detexit, illustravit P. Forskal. Hanniæ, 1775.

GEOLOGY.

In this sketch of the physical formation and natural history of the districts included in the basins of the Euphrates and the Tigris, we shall adopt the very natural and simple plan suggested by Mr. Ainsworth, when he observes that Assyria, including Taurus, is distinguished into three DisTRICTS: By its structure, into a district of plutonic and metamorphic rocks, a district of sedimentary formations, and a district of alluvial deposites: by configuration, into a district of mountains, a district of stony or sandy plains, and a district of low watery plains: by natural productions, into a country of forests and fruit-trees, of olives, wine, corn, and pasturage, or of barren rocks; a country of mulberry, cotton, maize, tobacco, or of barren clay, sand, pebbly or rocky plains; and into a country of date-trees, rice, and pasturage, or a land of saline plains.

First District.-That part of the Taurus which is connected with the basins of the Euphrates and the Tigris has been divided into three portions. The most northerly range comprises the Niphates Mountains; the central comprehends the Azarah Dag, and the mountainous country between Kebban-Madan and Kharput; and the most southerly, the ancient Masius, including the Karah-jah Dag, Jibel-tur, and the Baarem Hills. The central nucleus of these vast ridges consists of granite, gneiss, and mica-schist, associated with limestone, greenstone, and hornblende; the lateral formations are composed of diallage rocks, serpentine and slate clays, and the outlying ones of sandstone and limestone. The structure of the Niphates Mountains has not yet, we believe, been scientifically examined; the Azarah Dag chain is formed of diallage rocks, serpentine, steatite, and limestone; the Jibel-tur, of various limestones and the chalk formation; the Baarem Hills consist of greenstone and basalt. The most northerly range is probably the highest of the Taurus, towering above the line of perpetual snow, which in this latitude may be estimated at the height of about 10,000 feet; the crest of the second range, viewed as a mean between the highest points and the passes, is about 5053; and the plain of Diarbekir, between the second and third district, is at an elevation of 2500 feet.

We commence our more particular survey in the central range with the hills about Kebban-Madan, near the junction of the eastern and western branches of the Euphrates, and where the lead and silver mines occur. The town of Kebban, connected with the mines, is built upon granite rock, which extends downward to the banks of the river, and northward rises nearly a thousand feet in mountainous masses. The formations to the south of the town are very various. The fundamental rock is a highly crystalline granite, on which is superimposed gneiss rock, capped with chlorite schist, through which felspathic rock protrudes in dikes, or unconformable and non-contemporaneous beds. The first metalliferous product that is met with appears to be chlorite of silver, with an admixture of iron and lead; and it appears in dark-coloured irregular masses, like the formation of the same kind which overlies mines of native silver in Peru. Between the mica and chlorite slate and the limestone are numerous mines of argentiferous galena or lead-glance, a metallic sulphuret containing lead, silver in small proportions, antimony, iron, and red silver (sulphuret of antimony and silver). These mines are said now to yield 195,000 pounds of lead, and 1000 pounds of silver annually.*

a

Passing over, in our progress southward, the district of Kharput, where there is large plain extending south by west, we arrive at the copper mines of Arghana. The mountains which surround them have an elevation of from 4000 to 4500 feet; and Magharat, "the hill of caves," contains the principal mine. This eminence is composed of steatite, with veins of quartz, barytes, and asbestos of various kinds, the flexible, and the non-elastic; beds of limestone, sandstone, and copper pyrites. There are upward of fourteen galleries carried into the rock, and the annual produce is said to be about 2,250,000 pounds. In this barren region are situated the water-shed of the Euphrates and the Tigris, and the primary sources of this latter stream. To the north of Arghana there is a district occupied by carbonaceous marls and sandstones; and from this locality specimens of good coal were transmitted to the Euphrates expedition by Mr. Brant, her majesty's consul at Erzeroum.t Mr. Ainsworth, in his account of this locality, re

* Ainsworth's Researches, p. 279-281.

+ See Colonel Chesney's General Statement of the Proceedings of the

Вв 2

nous.

marks that the sandstone contained beds which were highly carbonaceous, and others that were distinctly ferrugiThe former were converted into stone-coal, with a vitreous fracture and dark shining surface; but they were non-bituminous.* He does not appear to have discovered any useful coal. Southward of this succeeds the plateau of Diarbekir, with a mean elevation of 1900 feet, and being for the most part a uniform flat, cut up towards the east by the Tigris. The rocks of the table-land of Jezirah, at an elevation of 1540 feet, are of the same mineral character, and consist of basalts with augite, titaniferous iron, and calcareous spar.

We may here remark, that neither the geological structure nor the correct topography of the Masius chain, including the Baarem Hills and Jibel-tur, have hitherto been described in a way that is at all satisfactory.t

We now proceed to the Second District, which extends from the thirty-seventh degree north latitude to the thirtyfourth, and comprises laterally the basins of the two celebrated rivers, from the confines of Syria to the mountains of Kurdistan, possessing a mean breadth of about 200 miles.

The character of the plains in this district varies with their latitude and altitude; with the quality of the soil, and the quantity of moisture. From Jezirah, westward to near Nisibin, there are felspathic plutonic rocks, with a mean elevation of 1550 feet, and which form a stony wilderness with little or no cultivation, but where, nevertheless, numerous flocks of sheep and cattle obtain a scanty support during a part of the year. The great plains of Northern Mesopotamia, from Orfa to Nisibin, and thence to the plain east of Mosul, the site of ancient Nineveh, have an elevation of about 1300 feet, are nearly of a uniform level, with a soil possessing good agricultural qualities, but barren for want of irrigation. An exception in regard to this sterility invariably occurs where the plains are intersected by hills or groups of hills-an arrangement by no means infrequent. As instances, we may specify the Babel Mountains, south Euphrates Expedition, in the Journal of the Royal Geographical Society, vol. vii., p. 438.

* Researches, p. 271, 272.

† See an interesting account of a journey in this district by Mr. Brant, in the Journal of the Royal Geographical Society, vol. vi., p. 208. In the accompanying map, the geographical aspect is better represented than in any other we have seen.

of Jezirah; the lower Kurdistan mountains, on the east of Mosul; the Sinjar range, bearing nearly west, and to the parallel of Nisibin; the Jibel Makhul and Jibel Hamrine, skirting the Tigris at Shirkat, stretching south and crossing it to the eastward, and extending thence far to the southeast; and the Southern Hamrines, which continue to the Persian Gulf.t The geognostic characters of these and other hills, and of the wide plains they overlook, will be briefly noticed when the districts to which they belong come more immediately under review.

The grand peculiarity of the whole of this vast region, in a geological point of view, is the fact that the tertiary, more especially those supercretaceous deposites which include gypsum (hitherto generally supposed to be confined to basins or circumscribed localities), assume an extent of geographical development which gives to them a scientific importance equal to that belonging to any other rock formation of the crust of the earth. The gypseous deposite is, moreover, divided into two great portions, characterized by a different association of beds, and separated by a great layer of marine limestones. The whole country, in fact, consists of these calcareous deposites, here and there interrupted by plutonic rocks.

The sedimentary masses which towards the south repose upon the plutonic rocks of the Taurus, are subcrystalline limestones, which, in the immediate neighbourhood of the mountain-chain, exhibit mostly a uniform texture, either compact or granular. At Samosata, the Euphrates runs through a valley from eight to ten miles in width, consisting of planes of slightly different altitudes, left by the river as it has at successive periods deepened its course. At Roumkala, the limestone becomes somewhat granular and splintery, arranged in thin strata, the upper beds being fossiliferous, having a high angle of inclination, much curved and contorted, and dipping in various directions, but most generally to the southeast. It is through formations of this character the Euphrates forces its way from Samosata to Roumkala; and its passage through these rocky portals is accompanied with much that is picturesque in scenery, and with phenomena highly instructive in science.

* For good representations of the Sinjar and Hamrine ranges, see map accompanying Mr. Forbes's and Lieutenant Lynch's Papers in the Journal of the Royal Geographical Society, vol. ix. p. 476.

† Ainsworth's Researches, p. 113.

« AnteriorContinuar »