STRUCTURAL GEOLOGY AND THE FORM OF THE GROUND. 17 



boulder clay groups, or, in some cases, to the soft variegated Jurassic 

 sandstones and alum shale underlying and cropping out from beneath 

 harder limestones of the same and of eocene age. The more tender and 

 saline rocks being reached by percolating water have yielded to the 

 wasting influences, and thus the harder masses above have been dislodged. 



The outer escarpments are thus always occupied by the older and 



harder rocks. Behind them is an enormous mass 



of the newer (Siwalik) tertiary soft sandstones, 



forming the whole of the Dangot, Lakargarh, and Shingarh mountains, 



the west side of the Maidan range, the north-west foot of the Khasor 



ridge, and all the Marwat hills except Shekh Budin gund. 1 



The Bannu plain occupies a basin formed by these newer tertiary 



Bannu plain, tertiary beds extending under the flat ground on all sides, 



tasin ' except the north, where its boundary coincides 



nearly with a fault, edged by a repetition of the scarped-anticlinal ridges 



elsewhere so pronounced. 



The plains of the Derajat and Indus 3 are a part of the great flat, 



mostly desert, which reaches hence to the Aravali 

 Deraiat. 



range and the sea in Lower Sind, doubtless wandered 



over in times past as they are now less extensively here, by the capri- 

 cious movements of the Indus, the Aba-sin, or " Father of waters "■ as the 

 great river is called in some maps. 



Whether these plains are in any degree due to marine erosion is a 



point so uncertain as to be beyond discussion here. 

 Marine plains. 



It cannot even be known whether the later mesozoic 



and tertiary deposits are spread horizontally beneath them in this region, 



or if the rocks which they conceal are disturbed. The original anticlinal 



structure of the different ranges adjacent, and the fact that the upper 



tertiary beds crossed the anticlinals towards the southward, afford grounds 



1 ' Gund ' means a distinct dheri, or hill. 



2 For further information relating to the plains of North-Western India, Mr. Medli- 

 cott's chapter on the Geology of the Punjab and its dependencies in the Government Gazet- 

 teer of the province may be consulted. 



b ( 227 ) 



