250 HASISADRA'S ADVENTURE vn 



barrows. For thousands of years, heat and cold, 

 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 long 

 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 alluvial 

 can be formed, the lowest limit (by 110 means the 

 highest limit) of age of the rivers can be deter- 

 mined. All such estimates are beset with sources 



1 It is probable that a slow movement of elevation of the land 

 t one time contributed to the result pvhaps does so still. 



2 At a comparatively recent period, the littoral margin of the 

 Persian Gulf extended certainly 250 miles farther to the north- 

 west than the present embouchure of the Shatt-el Arab. 

 (Loftus, Quarterly Journal of the Geological Society, 1853, 

 p. 251.) The actual extent of the marine deposit inland cannot 

 be defined, as it is covered by later fluviatile deposits. 



