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 
