5^ 



GRIESBACH: GEOLOGY OF THE CENTRAL HIMALAYAS. 



gradually from one into the other by alternating beds. The same 

 character distinguishes the Silurians in the entire area of the Central 

 Himalayas, in the most widely separated sections, namely, that 

 the predominant rock of the lower silurians is limestone, whereas 

 that of the upper is quartzite. 



Lower Silurian {4). 



Thelithological character of the lower silurian beds is very uniform 

 over the whole of the Central Himalayas; the pink and grey quartz- 

 schist and shales of the upper haimanta system passes gradually 

 into an alternation of dirty-coloured greyish pink quartzite, with 

 shaly calcareous partings, which again develops into a seiies of grey 

 shaly quartzites, alternating with dark blue to black Coral limestone. 

 All the calcareous beds contain fossil traces ; in the lowest beds of 

 this division, which is formed almost entirely of limestone and shales, 

 fossil remains are rare, and generally consist only of indistinct 

 casts of Or this and badly preserved Bellerophon specimens. 



In the upper beds of the lower silurians, and in the dark Coral 

 limestone, fossils -are very numerous and mostly well preserved. 

 Ivlost of the collections made by General Strachey, Mr. Hughes, and 

 in Spiti by Stoliczka, were derived from the lower division of the 

 Silurian. In common with the remainder of my Himalayan fossils, 

 these also await description, which I trust will ere long be completed. 

 This much, however, has already been ascertained that the fauna of 

 the " Coral limestone " division (4) is characteristic of the lowest 

 silurians of Europe. We have therefore a distinct horizon here, 

 which demies not only the position of the Coral limestone, but 

 also that of the underlying system of " haimantas," which must 

 represent pre-silurian deposits. 



The lower silurian is not of very great thickness. In the Niti 

 TK . , and Milam districts, I found that its entire 



Anickness. J 



thickness amounted to 300 feet only. It 

 appears that this is about the average thickness of the division in 

 almost all the sections which I have examined, where it was in 

 normal position and not much disturbed. 

 ( 56 ) 



