DESCRIPTIVE GEOLOGY: GENERAL CONSIDERATIONS. 275 



As to how this enormous concentration of acidic magmas along 

 the area now known as the Himalaya took place, and what were the 

 particular forces which first conduced to it, I cannot presume to offer 

 an opinion. Nor is it absolutely certain of course that there ever was 

 any such concentration of the material in its molten condition. 

 These granitic foundations out of which the Himalaya were ultimately 

 to rise may have been common to a very extensive area, by no means 

 confined to what is now the Himalaya. 



One fact must not be lost sight of in discussing this granitic or 

 Uniformity of petro- g neis sic rock, namely, its uniformity of petrolo- 

 logical characters. g j cal characters right through the Himalaya 



from end to end, so far as observations have gone. The particulars 

 I have given, page 62 et seq n as to its mineral composition, and struc- 

 tural features are not applicable to Hazara alone, but certainly to the 

 whole of the Himalaya that I know, and most probably to all the rest. 



If we turn our attention to the south of India, of t which I have had 

 some recent experience, what do we find is 



Compared with vari- 

 able gneissic rocks of the mineral composition of much of the gneissic 



tracts there? We find the felspar may be 

 variously coloured and of species ranging from orthoclase to 

 anorthite 1 ; we find the crystalline aggregates varying enormously in 

 the size and condition of the grains and in the resulting appearance 

 of the rocks ; we find the ferro-magnesian minerals may be not only 

 the micas, but also that hornblende and hypersthene play a great 

 role in these rocks ; and we find moreover that in certain areas cer- 

 tain bands across the country are characterised by the predominating 

 presence of one of these minerals and certain other bands by another. 

 There is no uniformity in S. India whatever as regards the 

 gneissic foundations of the peninsula, whereas this is the most 

 noticeable fact of all through the great — through the enormous-— thick- 

 ness of the corresponding crystalline rock of the Himalaya. 



For all then who prefer to view this rock as simply an extreme 

 effect of metamorphism of previously existing sedimentary iocks 



•As recently found near the corundum mines, Sithampundi. 



T2 ( 375 ) 



