34 TIIK PKlNCll'LKS < >F AGRICULirKK. 



and thaw several times, there will he found a pereeptihlc 

 quantity of Ihie ])arti('les at the hottom. 



13ut the greatest effeet of iee in fornihig- soil, and 

 changing the face of nature, has been through (jlaelers. 



In high, mountainous regions, and in cold latitudes, 

 snow steadily accunudates, forming immense masses of 

 ice in the deep valleys. These are steadily, but very 

 slowly, i)ushed along by their own weight until they 

 reach a lower and warmer region, where they melt away. 

 These huge rivers of moving snow and ice are called 

 glaciers. Rocks in the conrse of the glacier are torn up 

 and borne along, grinding npon one another, and grind- 

 ing paths through other solid beds of rock, until they 

 arc de])ositcd as bowlders and soil at the point where 

 the glacier melts. 



It is believed that, at some time in the history of the 

 earth, the regions to the north of the equator became 

 for a time much colder than at present, causing perpet- 

 ual snow to fall u])on large portions of North America 

 and Europe, deep enough to bury most of the hills and 

 mountains beneath vast, continuous glaciers. 



These glaciers, moving toward the equator, ground 

 enormous cpiantities of rock into soil, and deposited it 

 over a lai-ge extent of country, together with the rocks 

 wliich r(Mn:iin('(l ungrouud. Huge bowlders, as well as 

 smaller I'ocks, scattered over the country, ma\' be traced 

 back northward many miles, to their oi-iginal bed. In 

 New Euglaud they have been cai'ried two or three hun- 

 dred miles, and in the jMississi])])! Valley one thousand 

 miles. Soil and I'oci^s which have b(>en transported in 

 this way ai'c callccj (/;•//'/. 



5. ir/^/r/x. • — Winds have also taken some part in form- 

 ing soil, and espcH-ially in changing its location. In 



