ICE-PERIOD IN AMERICA. 
95 
around the northern and southern poles, stretch¬ 
ing thence over the northern and southern 
hemispheres to latitude forty, and that this 
field of snow acquires a thickness of from 
twelve to fifteen thousand feet. Such a mass 
would subside upon itself in consequence of 
its own weight; it would be transformed 
into ice with a greater or less rapidity and 
completeness, according to the latitude deter¬ 
mining the surrounding climatic influences 
and the amount of moisture falling upon it as 
rain or dew, the alternations of temperature 
being of course more frequent and greater 
along its outer limit. In proportion as, with 
the rising of the temperature, these alterna¬ 
tions became more general, a packing of the 
mass would begin, corresponding to that ob¬ 
served in the glacial valleys of Switzerland, 
though here the action would not be intensi¬ 
fied by lateral pressure ; an internal movement 
of the whole mass would be initiated, and the 
result could be no other than a uniform ad¬ 
vance in a southerly direction from the Arctic 
toward the more temperate latitudes in Eu¬ 
rope, Asia, and North America, and from the 
Antarctic toward South America, the Cape of 
