GEOLOGICAL FORMATIONS. 01 



approach an oblate rather than a prolate spheroid. Still the amount o£ 

 rounding is such as could only have been produced by a rapid stream. 



In Lower Sind, however, there is a very considerable intercalation of 

 marine or estuarine beds with the Manchhars, and this evidence o£ 

 deposition in salt water increases in the neighbourhood of the present 

 coast. Around Karachi, beds of oysters, and sometimes of other marine 

 or estuarine shells, are found not unfrequently interstratified with the 



Manchhar beds in Manchhar group. There is also some change in 



Lower Sind. ■• . , , , ■, , , 



mineral character, the sandstones becoming more 



argillaceous, and associated in places with pale-grey sandy clays and 



shales. The passage into the Gaj beds is very gradual, calcareous bands 



with Gaj fossils, such as Ostrea multicostata and Pecten suicomeus, being 



found some distance above the base of the Manchhar group. 



Although, on account of the change in mineral character, there 

 Relations to Gaj * s j except in the neighbourhood of the coast, no 

 S rou P- difficulty in drawing a line between Manchhar 



and Gaj beds, everything tends to show that there is no break in time 

 between the two, the lower portion of the upper group being an estua- 

 rine or fluviatile continuation of the underlying marine beds. But the 

 great thickness of the Manchhar group in Upper Sind alone would 

 suffice to prove that a considerable period of time must have elapsed 

 during the deposition of this formation, and it is far from improbable 

 that the lower Manchhar beds may be upper miocene, whilst the 

 upper Manchhar strata are pliocene. 



The Manchhar beds extend along the edge of the alluvium, and 



form a broad fringe to the Khirthar range, 

 Distribution. 



throughout Upper Sind, from west of Shikarpur 



to the Manchhar Lake ; but the breadth of the outcrop varies greatly, 

 being as much as 14 miles where broadest west of Larkana, and dimin- 

 ishing both to the north and south. As already noticed, the Manchhar 

 group is thickest just where its outcrop is widest ; but the breadth of the 

 area occupied by the beds is not due simply to their vertical development, 

 but chiefly to their forming a synclinal and anticlinal roll before disap- 



( 61 ) 



