44 MALLET : GEOLOGY OF DARJILING AND WESTERN DUARS. 



of the Darjiling gneiss, that both it and the Daling beds must be 

 younger than the coal-bearing rocks. It would be useless, however, in 

 the present state of our knowledge, to attempt to correlate them with 

 the known post-Damuda rocks south of the Ganges ; as, owing to their 

 altered condition, we are without reliable lithological, as well as without 

 fossil, evidence to base our conclusions on. 



It is scarcely necessary to add that the Darjiling gneiss must be 



_ ._. . ,. vastly younger than that of Bengal*, which was 



Darjiling gneiss dis- J ** ° ° . 



tinct from that of Bengal. f Q \\y metamorphosed and enormously contorted and 

 denuded before the Damiidas were deposited on it. The Darjiling gneiss 

 presents several points of difference lithologically. It is more quartzose 

 and the older rock more felspathic ; the felspar is, 1 believe, always white 

 in the Darjiling rock, while it is very frequently red in the other. 

 Again, the bands of dense tough hornblende rock which are so common 

 in the older formation, are absent in the newer, or only represented by 

 insignificant layers, and, as far as my examination goes, there is no lime- 

 stone or dolomite in the hill gneiss. The latter, at least in the Darjiling 

 district, is never granitoid as the Bengal gneiss so frequently is, and it 

 has a greater tendency to pass into, and contains more, mica-schist. 



Proceeding up the left bank of the Raidak river, the first rock met 



with is hornblende schist in thick beds dipping 



Bengal gneiss. 



north 10° west at 50°, and forming a low eminence ; 

 only a small thickness is seen. Beyond this is blank for a couple of 

 hundred yards, and then Tertiaries come in, dipping locally to north at 80°. 

 There can hardly be a doubt that this rock belongs to the gneiss which 

 forms most of the hills that are scattered over the alluvial valley of 

 the Brahmaputra, and which, according to Mr. Medlicott, there is no 

 reason to suppose is distinct from that of Bengal. The southerly trend 

 of the Tertiary hills both east and west from the debouchure of the 

 Raidak make it probable tRat the Tertiaries are not faulted against, but 



* The gneiss south of the Ganges is generally spoken of as the ' Bengal gneiss.' 



( 44 ) 



