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In the settle-down, the parallel zones, into which the sides of the vault were broken, would naturally assume an angle of dip much greater than was that of the vault previous to its fracture, as the sides of the Tanlt, in coming down again, would be submitted to considerable pressure, and therefore much redressed. It is not unlikely, therefore, that it is the effect of this pressure which has caused, in many mountains of the Himalayas, the appearance of younger rocks dipping under older, of felstone under porphyry, of schist and gneiss under granite.
The geologist must naturally expect to find a great many complications amongst these immense mountains. The view I have endeavoured to explain is a general one, and will, I hope, be better substantiated when we know more of the countries of the AfghanHimalayan system. With a little thought, I entertain a hope that the geologist, in finding apparent contradictions to what I have advanced, will always be enabled to discover the cause of the complication, at first apparently irreconcileable to my hypothesis.
There is one more remark to be made. The direction of the Silurian linear volcanoes of the Himalaya not being parallel to that of the Afghan chains, we have not a true anticlinal, but an oblique one. At the northern end of the axis of this oblique anticlinal, we have therefore a pressing of the sides one against the other, whilst at the southern end, we have a wide divergence of the ridges : at the northern end of the axis, we have the chains abutting one against the other, and thus supported at a great height; at the southern end we have the central beds unsupported and sunk down very low when the settledown took place; hence the high plateau of Pamer at one end and the low plains of India at the other. Again, when the Himalayan slope of the anticlinal was settling down, many of the great masses of porphyry, schist and gneiss resisted the general tendency to dip N. E., and caused a local fault to take place. This fault acted as the axis of an anticlinal for the locality immediately surrounding the mass of porphyry, schist or gneiss; and we find therefore such huge masses assuming the dip of the western branch of the Afghan-Himalayan anticlinal, or dipping N. W. Hence, the singular phenomenon, long ago noticed by Captain R. Strachey, that some of the great peaks of the Himalayas dip N. W., whilst all the beds round them dip N. E. It is also this same obliquity of the anticlinal' which has caused these numerous transverse faults observed in the Himalaya, which have a general direction from N. to S., and with the beds crushed one against the other at the northern end, whilst the fault gapes at the southern extremity.
All these phenomena, and several others which strike the naturalist as he travels through these mountains, appear to me to prove without a doubt, that the upheaving force was not applied at one certain point or along one certain axis, but that the whole country, now covered by the Afghan and the Himalayan mountains, was forced up into an immense dome or arch, which broke along certain lines determined by pre-existing volcanic zones, and settled into an oblique anticlinal, of which the slopes are sliced by a succession of parallel faults.*
98. It is a question of considerable interest to determine, with some precision, the epoch at which the great and last upheaval of the Himalaya occurred. We know that it was after the great mammals had become developed; and the extraordinary number of mammalian species found in the Sewalik hills would naturally induce one to consider a portion at least of what I have called the Tipper Miocene as older Pliocene. The Aralo-Caspian formation or steppe limestone, a brackish water deposit, has been placed by Murchison and DeVerneuil in the older Pliocene ; and one cannot help thinking that these shallow but immense inland or inter-insular seas must have existed previous to the final upheaval of the great mountains of Central Asia, and that it is indeed movements connected with this final upheaval, which have dried up the steppe-limestone and reduced these great seas to their present dimensions.
On the other hand, we have seen, that there exist in Thibet and in Ladak great beds of horizontal deposits, unconformable to the beds on which they abut, and containing fossil bones. Captain R. Strachey appears inclined to believe these beds to have been deposited previous to the upheaval of the Himalaya; but I think the hypothesis is not tenable, as it is impossible to understand how a " true sea-bottom
* The hypothesis (advanced, I believe, by Professor Ansted in his "Ancient World ") that the rising of Central Asia caused a depression in the Indian Ocean, marked by the cornl islauds of tho Lacadives, the Maldives, the great Chagos bank and some others, is ingenious j the depression, hewever, requires proving by actual observations.
ccmld have been uplifted from under the sea to an elevation of 15,000 feet," without losing its horizontality, whilst not only the beds on which the " true sea-bottom" rested, but the probable contemporaneous beds of the Sewaliks (according to Captain Strachey's hypothesis only,) are dipping N. E. at a high-angle. Captain H. Strachey describes the same bed, where it extends into Ladak, as old alluvinm, and mentions its containing fossil bones of extinct mammals. Captain Godwin Austen calls these beds, in Ladak, Rodok and Skardo, a fluviatile deposit. The bed is not limited to the belt of country situated between the Ser and Mer (Snowy Peak Range) chain and the Kailas chain. It is well developed in Rodok, near the Pang Chong Lake and up to the foot of the Korakoram chain, and it is very probable that the great Desert of Aksai Chin is a similar bed. I have said, in another place, that 1 believe these horizontal beds to be identical to the Ragzaier or elevated plateaux of the Afghan mountains. How were they formed?
In order to answer this question, let us consider what was the physical topography of the Himalayas soon after their final upheaval. There was not much difference in the configuration of the great ocean between the tropies; if we are to believe the geologists who have studied the Andes, these mountains had not yet appeared; the great plains of Africa, Arabia, Persia and India, were still under water; the mountains of the Indian peninsula may have appeared (and did probably appear at the time of the Himalaya's last upheaval) but were separated from the Himalaya by a considerable sheet of water; the great inland sea now represented by the desert of Gobi was not yet dry,—in short, there was little cause to diminish the humidity of the winds which blew from the south, and there was nothing to change their old direction. But the Himalayan and Afghan mountains were very different from what they had been. Instead of low ranges with volcanic peaks which did not probably soar above 5,000 or 6000 feet, we have now an immense wall, some hundred miles broad and 25,000 feet high, with deep longitudinal valleys offering no exit and much embarrassed by detached rocks and debris. The humidity of the winds which produced the tremendous rains of the Miocene period was now deposited as snow. Huge glaciers appeared and filled the longitudmal valleys, and the rivers which ran from them began to deposit a sediment which, in time, formed the great flat plateau of Thibet, Rodok, Aksai Chin, &c. &c. Thus we see the altered physical conditions which were brought about by the difference of elevation of the Himalaya, before and after its final upheaval. Before the upheaval, the humidity was collected as rain, and the mountain debris was washed to the coast by boisterous torrents; but after the upheaval, the humidity was collected as snow, and the mountain debris was quietly collected in the great valleys, under the cover of glaciers.*
All the while, a different action was going on in the outer or low Sub-Himalayau ranges. There the humidity continued to fall as rain and great denudation was the result. The same process of land gaining over the sea, which I have described at the Miocene epoch, began to form the plains of India; this process is still in operation now-a-days, but necessarily its power diminishes in intensity as the sea-coast becomes more distant from the hills and the course of rivers becomes longer. It is the process which is now anxiously watched by the pilots of the Hooghly, and which no engineering skill can avert: the sandbanks advance in the sea, the river-bed fills up, more dry land appears and what was yesterday a dangerous shallow out at sea, to-day is the shore of the delta, and to-morrow will be far inland.
As the plains of India extended, the rain-fall of the Himalaya diminished. Even if we suppose the humidity of the winds to have been the same as before, we must deduct from the Himalayan rain-fall the amount of rain which fell in the plains. Bnt we know that the humidity of the rains had also become less; the Andes had surged up and the South- American continent had appeared; the plains of Africa, Arabia, Persia and Central Asia were gradually appearing above the waters, and instead of the trade winds. the monsoons were establishing themselves. There was therefore a great diminution in the snow-fall on the Himalayas, and the glaciers began to decrease and to expose a great deal of the plateau on which they had gradually raised themselves. It is easy to understand how this decrease of snow-fall
• The filling up of the great parallel valleys of the Himalayas by mud and boulders, under the cover of the glaciers, is analogous to the filling up of dfpre.Hsions of the surface by the glacial drift in some parts of Europe. The glaciers of tho Himalaya, soon after the groat upheaval, were too hugo and too general lo have had a ploughing and scouring action on the valleys.
most have been very gradual, if we keep in mind what brought on that decrease; and as the glaciers retreated, animals advanced and soon populated the high plateau of the Himalaya. These animals have left their remains interred in the clayey grits of these elevated lands. It may appear strange that elephants once lived at such a great height, and in a climate so cold, but the osseous remains found in tho elevated plateau of Mexico belong to true elephants of extinct species,* and the Siberian mammoth which was covered by a warm fur, lived on the leaves of conifers and roamed over the ice-drift. There is therefore no doubt that these animals had a great plasticity of organism, and could adapt themselves to very extreme climates.
The mammals discovered in the plateau of Thibet and Ladak, all belong to extinct species. On the other hand, all tho shells which I have been able to collect in the old alluvinm found near the foot of the Sub-Himalaya belong to living species, and it is therefore most probable that the older alluvinm of the plains of India, and the high plateau of the Himalayas belong to the post-pliocene epoch.
From the above considerations, and the present state of our knowledge, it appears that the Afghan and Himalayan mountains suffered their last upheaval during the pliocene period.
99.—The description of the deposition of beds subsequently to the great upheaval has been given incidentally in the preceding paragraph; the glaciers began to melt, great lakes were formed in several localities. The Kashmir valley is a good example, Rukshu is another, and so is Abbottabad valley. These lakes at first fed large rivers, and both lakes and rivers had a considerable power in carrying mud, sand and boulders, and thus raising their beds by several hundred feet; but as the waterfall diminished, the lakes and rivers diminished also, and the rivers soon began to cut for themselves deep ravine-like beds in the middle of their ancient bottoms, leaving on each side a great river-terrace.
Before the rivers had lost their great volume, however, and while they filled the whole of their original beds, they floated icebergs of sufficient dimensions to carry blocks of stone of great size. The SaltRange for a time intercepted the free passage of the waters towards the south and a shallow lake filled the whole country between it and tho
* Cosmos, Otte's translation, Vol. I. pago 280.