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volcanoes this mass is perhaps upheaved daring their activity, but what is upheaved above ground is certainly but a small proportion of what remains underneath. This mass is covered by the materials which have flowed out and have spread themselves on the surface, either under the sea or in the open air. A great deal of this fluid material does never reach the surface, but finds its way into the cracks and fissures of the trachyte and porphyry. The portion which flows on the surface, whether in the air or under water is a lava; on the top of and interbedded with the lavas, scoriae, ashes, cinders, dust, broken rocks and mud, thrown into the air or into the sea by volcanic discharge?., are arranged in gentle slopes on the sides of the volcanoes and in flat strata further off. Now, let us suppose that the volcanic activity becomes dormant or ceases: we shall have under the spot where the volcano once broke out, great masses of melted and metamorphosed matter solidifying into various sorts of trappean rocks, while on the surface, stratified and fossiliferous beds will be deposited on the top of the lava and ashes. Should then the whole district be submitted to an expansive force acting from within outwards, this force will be first and most intensely felt by the great mass of underground porphyry and trachyte, which will be forced up and break through whatever covers it; the beds of basalt and amygdaloid through which it is forced, will be displaced and thrown aside or on their flank, dragging with them the stratified beds of cinders and fossiliferous strata. If instead of one volcano, we have many, situated not very far apart, we shall have the superficial rocks thrown into endless confusion by the upheaval of the many masses of porphyry and trachyte, which once formed their bases. The surging up of these masses of crystalline rock will of course diminish very materially the space occupied by the lavas, the cinders and the fossiliferous rocks at the time of their deposition ; and these have therefore no other alternative but to be broken in pieces, and these pieces to be raised more or less towards a vertical position, according to the quantity of rocks to bo packed in a given space. Thus, for example, near the Kaj Nag range, we have vast deposits of felstone well hemmed in, on the south, by an enormous thickness of passive tertiaries. When the huge mass of porphyry of the centre of this system of mountains received its last upheaval, it took possession of a great extent of ground formerly
covered by the felstone ; and this in its turn did its best to push the tertiaries further south, but this it only partially succeeded in doing; ami as there was much felstone and little room for it, tho bed broke into pieces and these pieces became packed edgeways.
82. Granite may be considered as the solidified matter of a volcano seated so far from the surface of the earth, that it never broke through its covering while the minerals were in a fluid or viscid state. It is the remains of a " blind volcano." Humboldt has described volcanic action, " the reaction of the interior of the earth on the external crust." This crust has to be broken through to allow of the escape of some of the internal matter; where the earth's crust resists the upward pressure, no crater is formed, no true volcano appears; but the melted matter remains imprisoned under the crust, and there gradually solidifies under great pressure. The solidification will necessarily be made more slow at a great depth, than it would be near the surface and near a rent which allows of the evaporation of the intermolecular water to take place; and it is the slowness of the cooling, the pressure sustained during the period of cooling, and the retention of intermolecnlar water and gases which cauRe the melted minerals to crystallise as granite and not as porphyry, greenstono or basalt.
83. In regard to their geographical disposition, volcanoes can be classified into "central" and " linear." The " central" are those which arise by themselves and appear not to be connected with any other volcano; the "linear" are several outlets arranged along a probable fissure in the earth's crust, and the fissure is often parallel to one or many other fissures similarly indicated by a line of volcanoes; or two fissures may cut one another obliquely, as we see in the Lipari Islands.
84. Applying the above general remarks to the volcanic rocks of Cashmir, we first notice that previous to the carboniferous epoch, there existed linear volcanoes arranged in a direction parallel to the present general direction of the Himalaya, viz. N. W. and S. E.; these volcanoes are now represented by the summits of Kaj-Nag and of the Kistwar and Badrawar and the peaks of the catenated chains of Cashmir. These volcanoes vary much in importance, but no doubt can be entertained of their general great activity, if we remember the enormous amount of ejecta which they have thrown out. The woll stratified arrangement of these ejected materials, especially those which are ejected in a loose and fragmentary condition, the amygdaloidal nature of nearly all the ash-rocks and some of the slates, and the existence of these slates interstratified with the volcanic rocks, justify the idea that some of the volcanoes were islands and others subaqueous craters, in a sea of moderate depth, and it requires no great effort of the mind to picture to ourselves an archipelago of fire-emitting islands in the Silurian sea.
At what time the volcanoes first out broke out, it is not at present possible to determine; they appear to have subsided at the beginning of the Carboniferous epoch ; and though phenomena related to volcanic power, in the most general acceptance of that term, were not wanting during and after the Carboniferous epoch, yet it is certain, as far as we at present know, that no regular volcano ever existed in the western Himalaya after the great Silurian volcanoes had become extinct.
85. It has been remarked in many parts of the world that, when a volanic district is, after the extinction of all craters, so disturbed that fissures are formed in the crust of the earth, these fissures do not pass through the old volcanic accumulations, but rather at a little distance from them. This has been explained by supposing that the masses of porphyry, trachyte and other once melted rocks,which have been ejected in the original volcanic fissures and amongst the rocks near this fissure, have so much strengthened the crust of the earth in the site of that fissure, that a new fracture takes place anywhere rather than across or along the old crack. If instead of one old crack we have many parallel cracks, the new fissures will then naturally take a direction parallel to the old fissures and will be situated between them. This has been the case in the Himalayas, and the great lines of fracture which were formed at the last upheaval, are none of them along the catenated volcanic chains, but between and parallel to these chains. But the catenated chains or lines of linear Silurian volcanoes determined the direction of the great lines of fracture which were formed at the last upheaval. We see therefore in the Himalayas great lines of fracture running N. W. and S. E., these fractures present a downthrow on the S. W. and the beds of rocks north-east of them form the great parallel chains of the Himalaya. The general dip of all these chains, and indeed of all the great beds of rock in these mountains, is towards the N. E.; an explanation of the cause of this dip will be given hereafter.
86. We have said that granite may be considered as the consolidated materials of " blind volcanoes;" that is, the cooled down masses of fluid or viscid matter propelled by internal tension towards the surface of the globe, but not with a force sufficient to overcome the resistance offered by the earth's crust. The soundness of this hypothesis appears supported by the metamorphic influence of granite over immense tracts of country: the conversion of shales, limestone, and sandstones and other rocks into gneiss, schist, marble and quartzite can only be explained either by supposing these shales, limestones, and sandstones to have been plunged deep into the bowels of the earth, there to be metamorphosed,—or else to have been the lid, covering and keeping under waves of fluid mineral matter. Now, the first supposition necessitates the assumption of very great disturbances of the earth's crust, of such disturbances as we cannot conceive or imagine by the analogy of anything we now see in the rocks of the surface of the globe. Neither is the idea of superficial stratified beds being plunged to a great depth into the earth, agreeable to the universal observation of a forcing-out power acting from the centre to the surface. The other supposition does not present the above-named objections: immense masses of melted matter may have approached sufficiently near the surface to have imparted great and. continued heat to the deepest stratified beds, and may have underlaid great tracts of country, without disturbing, to a very great extent, the position of the strata which they metamorphosed. Hence do we find beds of gneiss, schist and marble retaining great regularity of stratification for very many miles; so much so, that it has been possible to classify these metamorphic rocks in regularly snperposed formations, and to ascertain non-conformity between these beds, proving beyond a doubt their successive deposition.* It is impossible to understand how these beds could have preserved their relations, overa great extent of country, if it had been submitted, at one time, to a "bouloversement" so terrific and complete as to have plunged them under the solid crust of the earth, and, at another time, to the great upheaval necessary to bring them up again to the surface.
* The great example of this ia Sir W. Logan's Laorentian formations in Canada.
It is hardly necessary to add that the rolling of this great wave of melted minerals, under a certain part of the earth's crust, would set all the deep-seated waters to boil, would sublimate certain metals and elements, and that steam at a great heat, and occasionally impregnated with various vapours, would add its metamorphic influence to that of the heat disengaged from the molten granite underneath, and would here and their percolate and alter certain distant beds which would have otherwise escaped metamorphesis.
It has been advanced that steam alone was sufficient to account for the metamorphism; to me it appears inadequate to the work, when we come to consider the extensive beds of metamorphic rocks seen in several parts of the world. No Geyser, ever so hot, has yet been reported to have changed shales in its vicinity into gneiss or crystalline schists, though, I admit, the influence is often evident enough in beds of limestone. On the other hand, we know that dykes of greenstone, of basalt, or of amygdaloid have often converted sandstone into hornstone or quartzite, and slate clay into flinty-state or jasper. It appears therefore evident, that heat is one of the most powerful, if not the principal agent of metamorphism; it appears also necessary that the heat should be longsustained to produce such a great extent of metamorphosed beds as those we are considering, and that it should be equally and uniformly distributed. It does not appear likely that this persistent and uniform heat was supplied by bursts of vapours, nor indeed have we any analogy in the present days of large tracts of country being sensibly modified by the permeation of steam. The slow cooling of a mass of molten mineral under pressure would be admirably adapted to the work of metamorphosing the superincumbent crust, over several hundred square miles of country.
If the hypothesis advanced just now be accepted, we have no difficulty in understanding the graduating of granite into volcanic rocks; it is indeed what we would naturally expect to see, wherever subsequent upheavals have exposed extensive granitic and trappean regions.
To facilitate the application of these remarks to the Himalaya mountains, let us make a theoretical section from the south-west to the north-east across the Silurian Arohipelego of Kashmir and the sea to the north-east of it.