GEOLOGICAL FORMATIONS. 73 



dated into a calcareous conglomerate, forms a low slope, sometimes 2 or 

 4 miles in breadth, at the base of each range. This slope often covers a 

 large portion of the intervening valleys. On the flank of the Khir- 

 thar range, the deposit of gravel is usually well developed, being natur- 

 ally highest where streams issue from the range. Frequently, too, within 

 the range, remains of an old gravel deposit are seen covering portions of 

 the country at a considerable elevation above the streams, and sometimes 

 as near the Gaj, masses of gravel are seen capping isolated hills and 

 ridges in the neighbourhood of the main range. Such caps usually 

 exhibit a low dip away from the higher hills, and are manifestly unde- 

 nuded remnants of old gravel deposits. 



All such masses of gravel are more conspicuous in a barren country 

 like Sind than in better wooded regions, and similar formations occupy 

 an enormous area in Persia and other parts of Central and Western 

 Asia ; the great development of such deposits being apparently connect- 

 ed with the paucity of the rainfall and the absence of rivers of sufficient 

 size to carry away the de*bris washed to the foot of the hills, the rainfall 

 being sufficient to wash down such detritus where the slope is hio>h, but 

 not where the fall is diminished. 



The great plain north of Karachi is much covered by deposits of 



gravel and sand, often consolidated into hard con- 

 Plain north of Karachi. 



glomerate by carbonate of lime, derived from the 



pebbles of eocene and miocene limestone, of which the mass is largely 



composed. Near the coast, oysters of recent species, and a few other 



marine shells, are occasionally found in the conglomerate. 



Blown sand is found in many places on the plain of the Indus, but is 



far more abundant to the east than to the west 



Blown sand. 



ot the river. In the former direction it occupies 

 the vast tract known as the Indian desert. 



( 73 ) 



