PHYSICAL HISTORY OF THE AMAZONS. 425 



the Amazons exists to-day, it is widely open to the ocean 

 on the east, with a gentle slope from the Andes to the 

 Atlantic, determining a powerful seaward current. When 

 these vast accumulations took place, the basin must have 

 been closed ; otherwise the loose materials would constantly 

 have been carried down to the ocean. 



It is my belief that all these deposits belong to the ice- 

 period in its earlier or later phases, and to this cosmic 

 winter, which, judging from all the phenomena connected 

 with it, may have lasted for thousands of centuries, we must 

 look for the key to the geological history of the Amazonian 

 Valley. I am aware that this suggestion will appear extrav- 

 agant. But is it, after all, so improbable that, when Central 

 Europe was covered with ice thousands of feet thick ; when 

 the glaciers of Great Britain ploughed into the sea, and 

 when those of the Swiss mountains had ten times their 

 present altitude ; when every lake in Northern Italy was 

 filled with ice, and these frozen masses extended even into 

 Northern Africa ; when a sheet of ice, reaching nearly 

 to the summit of Mount Washington in the White Moun- 

 tains (that is, having a thickness of nearly six thousand 

 feet), moved over the continent of North America, is 

 it so improbable that, in this epoch of universal cold, 

 the valley of the Amazons also had its glacier poured 

 down into it from the accumulations of snow in the Cor- 

 dilleras, and swollen laterally by the tributary glaciers 

 descending from the table-lands of Guiana and Brazil ? 

 The movement of this immense glacier must have been 

 eastward, determined as well by the vast reservoirs of snow 

 in the Andes as by the direction of the valley itself. It 

 must have ploughed the valley-bottom over and over again, 

 grinding all the materials beneath it into a fine powder 



