DESCRIPTIVE GEOLOGY : SLATE ZONE. IOI 



A prominent distinction between the Slate series and the con- 

 glomeratic and shaley portions of the Infra-Trias in this locality is 

 that the latter shew no trace of any cleavage, whilst the individual 

 pebbles of which the conglomerate is made up each possess in this 

 locality the cleavage of the parent rock from which they were 

 derived. In view of other sections to the north of this where 

 the conglomerate has a cross-orientation of the long axes of the 

 pebbles (as in the Cambrian conglomerate of Snowdon) and a cleaved 

 matrix, this point is of considerable importance and will be refer- 

 red to again. 



When the top of the crags is gained the whole of the bare north 

 face of this part of the Sirban mass is seen to be sheeted by these lime- 

 stones which possess singularly marked and characteristic features. 

 They weather into a very white coloured rock, which is sometimes 

 vesicular, and generally banded throughout by layers of chert. The 

 joint planes are prominently developed, and appear as if made in some 

 soft material like wood by criss-cross strokes from a heavy sharp 

 implement. There are a few bands of coarse white grit or quartzite. 



It will be seen by reference to Waagen and Wynne's map and 

 figure 4, page 15, of their Memoir on the geology of Sirban, that these 

 rocks are represented as Infra-Trias only up to a certain line running 

 east of Mehra village, beyond which the greater part of the north face of 

 Sirban is classed with the Trias formation. In the course of map- 

 ping this hill I found no reason whatever for this arbitrary line of divi- 

 sion, and good reasons both lithological and structural for the alter- 

 ations I have been compelled to make in the mapping of this part. 



As this will be found to be the greatest point of difference be- 

 tween myself and Mr. Wynne in the mapping of Hazara, it is 

 perhaps necessary to explain my reasons for a change that makes 

 a large alteration in the geological features of Sirban. They are : — . 



(1) All these limestones which sheet the hill-side are always found 

 (when they are found at all) in normal order superposed on the 

 top of the typical Infra-Trias (conglomerate, shales, sandstone, and 

 deep purple limestone). On the other hand, they are never found 



( 101 ) 



