GENERAL CONSIDERATIONS. 1 27 



But, besides the direction of disturbance not always being the 

 same, the amount of it is very dissimilar in the two rock groups. 

 The older rocks exhibit a very much more intense and prolonged 

 crushing than the younger Tertiary rocks. This is represented by 

 the dynamic metamorphism to which the former have been subjected. 

 Examples of plutonic, volcanic, and sedimentary rocks which have all 

 undergone intense crushing, with production of either cleavage, 

 augen or lenticular-tabular structure in them, have been given by me 

 in the Records. 1 Ordinary granite is very seldom to be met with : 

 it has nearly always been converted into gneissose-granite, the indi- 

 vidual felspars having been crushed into one another until the rock 

 assumed a lenticular banded appearance. Some basic plutonic rocks 

 have suffered in the same way. It is also difficult in many places to 

 find a normal unaltered trap ; and the rock is sometimes so much altered 

 as to be scarcely recognisable. Quartzites, containing pebbles, have 

 also been described as converted into quartz-schists ; the different 

 grains of quartz having been broken and run together into lenticular 

 bands, like the crystals of felspar in the gneissose granite, and films 

 of mica developed between them. All these peculiarities bespeak age 

 and intense dynamic metamorphism. And there are no like evi- 

 dences among the Sub-Himalayan rocks. The latter have been crushed 

 and contorted as to their strata ; they have been wrapped into im- 

 mense sigma-flexures, and cut up by reversed faults ; but of cleavage 

 and (fynamic metamorphism they show no sign. 



In his memoir, Mr. Medlicott declared his belief in the distinct- 

 ness of the disturbance which upheaved the main Himalayan chain, 

 and the disturbance which in later times affected the Sub-Himalaya. 

 He wrote 2 " These remarks lead me to the conclusion that the fea- 

 " tures of disturbance in these youngest rocks have no direct connec- 

 tion with the formation of the mountains. But connection there 

 " most decidedly is. I believe the disturbance of these rocks to be 

 "entirely a reflex effect. As the composition of the Siwalik strata 

 " and their enormous accumulation give evidence of the vast denuda- 



1 Rec, G. S. I., XXI., p. 11. 3 P. 169. 



( 185 ) 



