Chap. VI.] general structure of hills. 3 61 



rocks, which he supposes to be separated from those inside them by a 

 series of great faults, and then passes to the description of the argilla- 

 ceous schists and limestones associated with trappean rocks, which form 

 a continuous belt along the outer limits of the Lower Himalaya. His 

 description next embraces a broad tract of mica-schists, in which occurs 

 a run of granite, showing intrusive action along the lines of its contact 

 with the schists. In the northern part of this band of sub-metamorphic 

 rocks, he notices three changes of dip with dislocation of the strata, and 

 in one case trappean intrusion ; in this part of the zone also limestone 

 is common. The zone of partial metamorphism, his description goes on 

 to say, is succeeded on the north by the band of thoroughly crystalline 

 schists, in which occurs the line of peaks. Along this line there are 

 invariably seen, for a breadth of several miles, veins of granite in great 

 abundance, penetrating the schists, often cutting through them, but most 

 frequently following the bedding, in which the same general dip, as else- 

 where, to the north -north-east, is pretty constantly observed. In some 

 places, he states, the granite forms whole mountains. In this region also 

 beds of limestone are of frequent occurrence, always highly crystalline. 

 Along the north side of the line of peaks the schists are overlaid by 

 slaty rocks, about 9,000 feet thick, the bottom beds of these are 

 coarsely conglomeritic, and are also to some extent penetrated by granite 

 veins, but on the whole the contrast with the gneissose rocks is well 

 marked. The slates are followed, he says, in regular succession by about 

 6,000 feet 'of palaeozoic rocks, consisting of limestones, slates, and 

 grits, capped by quartzites, which form the peaks of a second line of 

 ridges. Still further to tfee north we are brought to the lower and 

 middle secondary rocks, principally limestones, 5 or 6,000 feet in 

 thickness, showing parallelism of dip and strike with the rest of the 

 section. In the upper part of this section the frequent occurrence of 

 eruptive greenstones is noticed, and that the rocks begin to be covered 



by the deep superficial deposits which form the great plateaux of Thibet 



w 



