104 GRIESBACH : GEOLOGY OF THE CENTRAL HIMALAYAS. 



rather as a series of beds having similar lithological character and 

 distinct fossil remains. 



•. , ., . The silurian system may therefore be said to 



Divisions of Silurians J •> 



in the Silakank section. consist of the following principal divisions : — 





Number in 



the figured 



sections. 





Upper silurian about 1,100 feet 

 thickness. 



5 



Alternation of dirty pink and flesh-coloured 

 quartzite with dark-blue limestone. 



Alternation of flesh-coloured quartzite with 

 greenish grey shales. 



Lower silurian about 200 feet 

 thickness. 



4 



Coral limestone with greenish shales and 



quartzite. 

 Concretionary dark limestones with Corals 



and flesh-coloured quartzite. 



As will be seen, the prevailing rock of the silurian system in this 

 section is a flesh-coloured to brown quartzite with fossils ; this type of 

 beds is best developed in the centre part of the system, and with it is 

 associated near the base, Coral limestone, towards the middle of the 

 section greyish and green shales, and towards the top, concretionary 

 dark-blue limestone. The passage from the highest beds of the 

 silurian system, into the overlying devonian or lower carboniferous 

 Coral limestone, is gradual and single beds of flesh-coloured quartzite 

 are found high up the series of limestone and shales which, I believe, 

 belong to the carboniferous system. 



The above section is almost the only instance I have met with 

 during several years' work in the higher Himalayas, which permitted 

 an easy and nearly accurate measurement of the thickness of its 

 several beds to be taken. At other localities I found the lower 

 palaeozoic formations either greatly folded and crushed, or partially 

 hidden by masses of glacier ice and snow, and preventing thus even 

 an approximately accurate estimate of their total thickness. But I 

 consider the Pethathali section a fairly representative one, and I may 

 here mention that I have found almost identically the same beds at 

 localities widelv separated, such as, for instance, Spiti and Dharma. 

 The silurian rocks form the lowest part of the steep cliffs on both 

 ( 104 ) 



