descriptive geology: general considerations, 279 



ltog over such a wide extent of country, have been given in chapter 1 

 II. This dynamic metamorphism of the crystalline rocks is, indeed, 

 a very real thing, most striking to the geologist who visits the Hima- 

 laya for the first time. Every crag he comes across is remarkable 

 for its parallel foliation and for its most evident fissibility. Every 

 rock fragment he finds strewing his path is in the form of sheets and 

 slabs for the same reason — in consequence of which such slabs are 

 almost universally used by the natives for roofing purposes — though 

 they are heavy material enough thus used. In addition to this, he 

 may frequently wander for miles along river-beds and gorges with 

 Walls or rather banks of rock all round him absolutely so sheared 

 and so powdered up that it is next to impossible for him to find suffi- 

 cient sound rock to make a specimen. 



Just as the mineral composition of the great crystalline axis of 



the Himalaya has been found to be the same 

 Constancy over the 



full length of the Hima- right through from end to end of the chain, so 

 is it also found to be the case that the dynamic 

 metamorphism of those rocks is also a constant factor throughout the 

 range. 



I do not think there can be two opinions as to the origin of this 

 state of things. It can only imply a steadily 

 Its cause. acting lateral pressure of the earth's crust tend- 



ing to bank it up against the central crystalline core by a movement 

 and a resistance in two opposite directions. To the south we have 

 the newer zones of disturbance shewing no dynamic metamorphism, 

 but to the north the accumulated pressures consequent on the up- 

 heaval of several zones one after the other, with the gradually 

 diminishing in size of the larger earth folds as the centre of the solid 

 crystalline core is approached, have all tended to bring about that 

 intense cleaving, shearing, and deformation of the minuter particles 

 of the rock which I embrace generally under the head of dynamic 

 metamorphism. There is no need, I think, to make any assumption 

 as to the particular points of departure for the various stresses. 

 From whatever points or lines they proceeded, their effects would be 



the same. 



( 279 ) 



