GEOLOGY. 41 



This may nevertheless be going on in favourable situations, as is 

 said to be the case in a land-locked arm of the Caspian j* or, as has 

 been suggested with regard to the Red Sea, notwithstanding that deep 

 ocean soundings in recent years have not borne witness to the fact. 



In discussing the circumstances of the salt region under notice with 

 Dr. Warth, it appeared that if a column of sea-water may deposit 

 y^th of its volume of solid saltf it may be roughly calculated that to 

 produce the two square miles of salt taken at J-th mile thick at Bahadur 

 Khel, a volume of sea water of the same depth and 100 square miles in 

 area (equal to twenty cubic miles) would be required, and this should pro- 

 bably be evaporated to half its original bulk before deposition of salt 

 would commence. 



If the whole of the salt deposits be considered to represent a series 

 of brine pools formed by the slow desiccation of a once continuous sea, 

 the area within which they occur being one of about 1,000 square miles, 

 and the salt presumably present over more than jth of this area, or 200 

 square miles, this sea may have had a depth equal to the unknown thick- 

 ness of the salt deposits in most of the districts, and a superficial extent 

 of 1,000 or 2,000 square miles according as it may have been deep or 

 shallow, while if the rock salt be, or was once, conti nuous from one ex- 

 posure to another over the whole area of 1,000 square miles, the extent 

 of the depositing sea may have been from 50,000 to 100,000 square 

 miles. 



* At Kara Bugaz (?) {i. e., The Black Gulf), eastern side of the Caspian. The accu- 

 mulation of the salt in this case may be gradually increasing, but it is by no means clear, so 

 far as can be learned, that the sources of the salt supply are not traceable to the rock-salt 

 stated by Karsten to occur extensively on the eastern borders of the Caspian rather than 

 merely to its own waters. 



f Bischof (quoted by Jukes in his Manual, p. 137,) gives saline matter in sea-water as 

 3'527 per cent., of which 75*786 in 100*000 is chloride of sodium. Taking sea-water to 

 contain sixteen times as much salt as gypsum (same authority), it is curious to note the simi- 

 larity of this ratio to that between the calculated thickness of the salt and gypsum in the 

 Bahadur Khel exposure. 



f ( 145 ) 



