250 ii ASISADRA'S ADVENTURE \ u 



barrowa For thousands of years, heat and 

 rain, snow, and frost, the scrubbing of glaciers. 

 and the scouring of torrents laden with sand and 

 gravel, have been wearing down the rocks of the 

 upper basins of the rivers, over an area of many 

 thousand square miles ; and these materials, 

 ground to fine powder in the course of their L.HL; 

 journey, have slowly subsided, as the water which 

 carried them spread out and lost its velocity in 

 the sea. It is because this process is still going 

 on that the shore of the delta constantly en- 

 croaches on the head of the gulf 1 into which the 

 two rivers are constantly throwing the waste of 

 Armenia and of Kurdistan. Hence, as might be 

 expected, fluviatile and marine shells are common 

 in the alluvial deposit; and Loftus found strata, 

 containing subfossil marine shells of species now 

 living, in the Persian Gulf, at Warka, two hundred 

 miles in a straight line from the shore of the 

 delta. 2 It follows that, if a trustworthy estimate 

 of the average rate of growth of the alluvK 

 can be formed, the lowest limit (by no means tl 

 highest limit) of age of the rivers can be det 

 mined. All such estimates are beset with soui 



1 It is probable that a slow movement of elevation of tin- 1; 

 at one time contributed to the result perhaps des M still. 



* At a comparatively ivrrnt period, the littoral margin of tl 

 :M dull extended certainly 250 miles farther to the nortl 

 west than the present embouchure of the Shatt-el Aral 

 (Loftus, Qimi't'-i'lii Journal of the Geological Society, I8i 

 p. 251.) The actual extent of the marine deposit inland 

 be defined, as it i.s covered by later fluviatile dep. 



