128 GRIESBACH : GEOLOGY OF THE CENTRAL HIMALAYAS. 



I measured the section of the Spiti shales of the Sirkia area as 1,350 



Thickness of Spiti ^ eet > though I believe the actual thickness to 



shales near Sirkia. ^ j ess> There is a good deal of local crushing, 



and in the soft friable mass faults are not easily detected or can be 

 allowed for. 



The general sequence of beds is much the same as previously 

 observed in the Sherik river. In the lowest portion I found numer- 

 ous Ammonites in the nodules, chiefly Triplicati, Bifurcati and 

 Coronati. Above follow nodules with many Belemnites, sometimes 

 whole nests of them. Posidonia and other Bivalves also are numer- 

 ous. This portion of the shales is again overlaid by a horizon in 

 which the nodules yielded chiefly Ammonites, but the shales were 

 getting gradually less rich in fossiliferous nodules and more ferru- 

 ginous. Partings of clay iron ore, and strings of ferruginous con- 

 cretions become common. Near the camp in the upper portion of 

 the Spiti shales, fossils disappear almost altogether, or are only pre- 

 served as crushed fragments. The shales are now more evenly bed- 

 ded, some portions intensely black, then again showing numerous 

 ferruginous partfngs, between which the shales are dark grey, mostly 

 micaceous, and not unlike some of the Gondwana shales in lithological 

 appearance. 



About 500 yards north of the camp, close to the junction of the 



Sirkia with the Sherik streams, high cliffs face 

 Cretaceous of Sirkia. 



southward (see fig. 11). They are formed of 



beds dipping about 35 north-east. The Sirkia river has excavated 



a narrow and very picturesque gorge through these beds and so 



exposed a perfect section of them. Near the junction of the two 



rivers the upper Spiti shales are beginning to alternate and pass into 



a thin bedded grey sandstone, the strata of which vary from 4" to 8" 



in thickness, become gradually more silicious, until near the base of 



the high cliffs north of the Sherik river it is a grey quartz sandstone, 



weathering a rusty brown, alternating with silicious greenish shales, 



which higher up again pass into a flaggy greenish grey quartzite. 



This rock continues northward through the gorge of the Sirkia 



( 128 ) 



