1873.] BLANF0RD — PERSIAN SUPERFICIAL DEPOSITS. 501 



plains would be gradually washed down to the lakes ; then a great 

 part of Central Persia would become a vast lake. • Finally, as the 

 water increased, the barrier of surrounding mountains would be cut 

 through, probably in several places, and the lakes drained, whilst 

 the country would be converted into a series of ordinary river- 

 basins. All this is precisely the converse of what I believe to have 

 taken place during the desiccation of the country, except that there 

 is no reason for supposing all Central Persia to have been one lake 

 at any time. 



Of course the original denudation of the great valleys and basins 

 of Persia must go back to an earlier date than that of the supposed 

 lakes — to a time when these valleys were open to the sea, and were 

 cleared out by running water. Such valleys were probably dammed 

 up by the rise of land in Southern Persia at a time when the rain- 

 fall no longer sufficed to keep the channels open. That the eleva- 

 tion of the Southern-Persian mountains is of no high geological 

 antiquity we may infer from the fact that ranges 10,000 feet high 

 consist of nummulitic rocks, that the gypsiferous beds, which are 

 newer than the nummulitics, are found at an elevation of 7000 feet 

 above the sea*, and that the Makran formations t, which are pro- 

 bably not older than Pliocene, attain almost an equal height ; whilst 

 traces of a recent rise of land are common along the southern coasts 

 of Persia and Baluchistan. 



Conclusion. — The general results of the facts which I have 

 endeavoured to describe may be briefly summed up. I think it 

 probable that Persia is a country which has undergone a gradual 

 process of change from a moister to a drier climate, simultaneously 

 with the elevation of portions of its surface, resulting in the con- 

 version of old river-valleys into enclosed basins containing large 

 lakes, many of them brackish or salt ; then, as the rainfall dimi- 

 nished, the lakes, for the most part, gradually dried up, becoming 

 desert plains ; and the process of disintegration amongst the rocks 

 of the hills exceeding the powers of removal, the water which now 

 falls only suffices to wash the loosened rock-fragments from the 

 steeper slopes of the hills into the valleys, not to transport them to 

 the lowest levels of the country. The consequence is that the upper 

 parts of the great valleys are being gradually filled up with coarse 

 gravel-like detritus, just as their lower portions have already been 

 hidden beneath lake-deposits. 



In the accompanying map (p. 499) an attempt has been made to 

 delineate roughly some of the lakes which once, I believe, covered 

 a large portion of the Persian plateau. The supposed lake-areas 

 are indicated by the tint. Prom the want of detailed information 

 the lines laid down are, in most cases, mere approximations. For 

 most of the information embodied in this map, as well as for nume- 

 rous details scattered through the preceding pages, I am indebted 

 to my friend Major O. B. St. John. 



* Loftus, Quart. Journ. Geol. Soc. vol. xi. p. 334, fig. 11. 

 t Records of Geol. Surrey of India, vol. v. p. 43. 



