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This theoretical section shows ns a succession of volcanic islands or maritime or sub-aqueous volcanoes of which the base is a mass of melted matter, destined to solidify as porphyry, trachyte and other volcanic rocks, whilst the melted materials situated further from the vents are to solidify as granite. Over the granite, we find the crust more or less intact, though metamorphosed into gneiss, schist and marble; over the porphyries and trachytes we find that it has been removed and torn up by the ejecting power of the melted mass making its way to the vents. Over and between the volcanoes, we find a very thick bed of ashes, broken stones, agglomerates and lavas. Over the granite we find, after the gneiss and schists, stratified deposits of Silurian shales and limestone. After the extinction of the volcanoes, we find the whole sea-bottom covered with the fragments of animals of the Carboniferous period; and thus do we see in Kashmir the Carboniferous limestone resting conformably on the volcanic rocks, and not disturbed by their intrusion.
Of course many changes, oscillations, denudations and depositions took place between the extinction of the Silurian volcanoes and the great final upheaval of the Himalayas; but these changes do not appear to have been on a sufficiently grand scale to have affected, to any great degree, the lithological features of the earth's crust, in the portion of the globe wc arc considering. At the final upheaval, a series of new fissures were formed and are represented in the diagram above, and the position assumed by the several slices, between these fissures, is represented by the dotted outline. There are many more parallel fissures, I have no doubt, but they did not cause a great upthrow of one of their edges, and have therefore little to do with the general configuration of the Himalayas.
The position of the fissures, between the old volcanic lines, and not on them, has produced the phenomenon that nearly all the highest peaks of the Himalaya are not situated on the chain to which they belong, but a little distance from it. The fissures, taking place in the weakest parts of the crust, followed the old valleys between the lines of volcanoes, and the volcanic masses are therefore superior to the chain formed by the edge of the fissure by the height these volcanic masses originally possessed. It is also reasonable to admit that the movement of upheaval was more powerfully felt by huge masses of prophyry, trachyte, granite, gneiss, etc., which cannot be easily compressed or folded, than by the flat beds of dusts, slates, lavas, ashes and fossiliferons rocks.
87. Glancing now at the Afghan mountains, we find that their chains have a steady direction from the north-east to the south-west. We find also that, as far as has been ascertained, the dip is invariably a. W. or W. N. W.; that is, presents the same phenomenon as in the Himalaya, of the beds of rock rising towards the plains of India. This dip is that of all the rocks of the trans-Indus districts; it is that of the beds in Verziristan, and of most of the nnmmulitic strata in Hazara, and indeed, wherever it has been possible to examine it, it has been found to be north-westerly. We cannot therefore refuse to admit, that the strike of the Afghan mountains meets the strike of the Himalayas, and the dip of the latter being North-easterly and that of the former North-westerly, wo are justified in concluding, that the whole of these huge mountains forms one and the same system of upheaval; that a tremendous dome or swell did surge up in the region of our Silurian volcanic archipelagoes, and that the Himalayas on one side and the Afghan mountains on the other are faulted slopes of a gigantic oblique anticlinal!
A true anticlinal it cannot be called; it is more properly the result of an incalculable force pressing outwardly the crust of the earth and endeavouring to raise it into a dome ; and as such a dome could neither he raised nor settled down again without much fracturing of the crust of the earth, the lines of fracture followed the direction of the old volcanic lines, and on one side ran N. W.— S. E. (Himalayas) and on the other N. W.—S. E. (Afghan mountains).
No good explanation has yet been advanced of the general N. E. dip of the Himalaya; none has even been attempted of the N. W. dip of the Afghan mountains. By placing the axis of the dome between these two masses of mountains, and considering these mountains as the opposite jambs of an oblique anticlinal, the singular dip ■of both is satisfactorily explained.
88. PI. XI. is intended to give an idea of the great fissures of the Afghan-Himalayan system of mountains.
We must not forget that the fissures went through portions of the crust, having a much greater power of resistance in some places than in others, being here brittle, there tenacious, here rigid and there easily bent; and we must not expect too much regularity in the fissnres, but be prepared for occasional deviations from the general direction. The Miocene beds, which present the greatest uniformity of formation, have everywhere the most regular strike, in spite of their numerous foldings and faults; the great beds of felstone are also tolerably regular in their general dip, and so are the great beds of Carboniferous limestone in Kashmir, though of course the smaller beds, especially those close against high summits, have a local dip and strike. The interminable masses of metamorphic schists, described by travellers in several parts of the Himalayas, have also a steady N. E. dip, and Captain R. Strachey tells us that in that portion of the Himalayas which he examined, the N. E. dip was the general one. On the Afghan side of the oblique anticlinal the Miocene again presents the greatest regularity, and the Nummulitic formation nearly equals it; the dip of both these formations is very steadily towards the N. W.
Another cause which has no doubt contributed to break the uniformity of the parallelism of the chains is the pressure, in some places, of such enormous accumulations of volcanic porphyry as we see at the Kaj-Nag and in Kistwar and Badrawar. These centres of volcanic rock appear to have been very huge; they were undoubtedly solidified long before they became upheaved, as they were formed during the Silurian epoch, and did not receive their upheaval until the Tertiary period had been nearly run out. They were, therefore, raised up bodily as solid masses, and they had been too huge to arrange themselves in the general parallelism of the fissures. I have represented them in the plate as huge centres of volcanic action, regarding them as too enormous to be displaced by even the force which has uplifted the great dome of the Afghan-Himalayan system; they were merely forced up. The Sufed Koh and the Koh-i-Baba in the Afghan mountains occupy a similar position in relation to the parallel chains; the first named is probably a volcanic mass, and I have assumed that the other is likewise a porphyry centre. It is probable that certain granite masses have acted in a like manner; but it would be of littlo profit to speculate about those masses, knowing at present nothing positive regarding them.
The fissures just describeil being once formed, we have no difficulty in understanding how the slices of crust between them were compelled to remain in an oblique position, viz. dipping N. E. and N. W. respectively, when the settlement took place, if wo remember, that a great deal of granite, lignite, porphyry, trachyte, &c. buried under the surface before the upheaval, had now been forced up and occupied a great portion of the room; unable to find space enough to resume a horizontal position, these bands of the earth's crust became impacted in the position we now see them.
89. Coming down from the high regions of the Himalaya and of the Afghan mountains to the Salt Range and the hills of the district oi Bunnoo, we notice the interesting phenomenon of the tilting up of the angular extremity of the piece of crust that had been broken off, between the converging fissures of the Sub-Himalaya and the SubAfghan hills. This crop-fracture is just such as we see near tho point of an angular piece of a window-pane which has been starred by a blow. The dip of the Salt Range and the Bunnoo hills is consequently disposed in a somewhat converging manner, such as is indicated by the arrows in PI. XI.; tho crop fracture is not a straight line; it is a succession of segments of a circle, and the dip of each segment is converging more or less towards the centre of its circle.
It is, however, possible that this breaking of the tip of the triangular piece of crust is only apparent, and that the segmentary and converging dip oi the beds may be due to a complexity of resultant forces, at the place where the N. W. and N. W. dips meet.
To the south of the Salt Range extend the vast plains of the Punjab, Ajmeer and Marwar, covered mostly with clay and sand, often a desert without a hill or even a mound to relieve the monotony, and with hardly a pebble to be found for some hundreds of miles. So far south as Lat N. 27° these great plains extend without a break, and then we find the volcanic rocks of Central India, supporting hero and there beds of sandstone with mammalian bones* similar to those which are so well developed in the Sub-Himalaya and Sub-Afghan ranges. Whether the whole, a portion, or none of the volcanic rocks of Central India are contemporaneous to those of the Himalaya, I know not,
* Bones of extinct mammals have been found in tho Valley of tlio Nerbudda, South of Lat. N. 21°, no Miocene haa ever been found.