A GRASP OF GEOLOGIC TIME. 157 



eral centuries before our era. Any one who will take 

 the trouble to consult Rawlinson's Herodotus will find a 

 map of the Scythian plains in which the Sea of Azof pos- 

 sesses still an extent approaching in area even that of 

 the Euxine itself. History has not brought us equally 

 explicit tidings of the contraction of the Caspian and Aral 

 Seas; but geological and topographical evidences proclaim 

 with unmistakable clearness the recent retreat of the 

 Caspian on the north, over a distance of 240 miles of 

 country depressed below the present sea-level, and many 

 hundreds of miles of territory but little elevated above 

 it. Indeed the opinion prevails that in times geologically 

 recent the Caspian was joined to the White Sea and the 

 Sea of Obi, and the Aral formed part of the same body 

 of water. When the Caspian flooded the valley of the 

 Volga the Euxine filled the valleys of the Don and 

 Dnieper. The plains between these two rivers were then 

 sea-bottom as well as the Ponto-Caspian flats north of the 

 Caucasus and stretching from the Sea of Azof and the 

 Don to the Caspian Sea. Thus, in times comparatively 

 modern, a vast region stretching from Turkestan to the 

 Danube and from the Elburz Mountains to the White 

 Sea and the Sea of Obi has constituted a part of the 

 water-surface of the earth. Here has been a geological 

 emercrence of almost half a continent, the later stagjes of 

 which mankind stood by to witness, and the recollection 

 of which lingered in tradition and then in history till 

 science has arisen to bring full confirmation.* 



There are indications not a few that the delta of the 



* See Von Baer. Kaspisrhe Studien, and Wood, Tlie Shores of Lake Ara', 

 1876 ; Sir R. Murchison and Sir H. Rawlinson, Jour. Hoy. Geogr. Soc, 1867; 

 Roesler, Die Aralseefrage, 1873. 



