82 Evolution of the Earth. 



der, dislodging portions, and creating larger crevices and 

 fissures. Masses of the rock are undermined, and fall, and 

 are pulverized by the subsequent weathering. In this way- 

 rain, snow and frost are continually at work, making soil 

 and other forms of detritus from rocks. Some such process 

 as this went on during those early periods before life and 

 vegetation appeared on the earth ; for life and vegetation 

 demand soil, and all the soil which now covers vast areas 

 of the earth's surface was originally made by slow processes 

 of disintegration and attrition, from the rocks. Only, in 

 those primitive times of which we speak, the rocks were 

 not the same in character as those of the Palisades — those 

 the world over on which the forces of nature are acting to- 

 day ; — for these in their turn, or most of them, have been 

 formed from the detritus of disintegrated rocks by processes 

 hereafter to be described. The earlier soil, as well as the 

 atmosphere, was, therefore, of a different character from 

 that of to-day, adapted to the production of a coarser, more 

 luxuriant, less delicate and beautiful vegetation. If we 

 take a section of the material which lies at the bottom of 

 any high cliff like the Palisades, or around the bases of 

 mountains, Ave shall find that it is composed of the same ma- 

 terial as the cliff or mountain above. Thus, partly by at- 

 mospheric agencies, by rain, frost and snow, by the action 

 of the sea as it breaks against the cliffs along the shore, 

 partly by glaciers — those rivers of ice, which slowly, but 

 with tremendous energy, wear their way down from moun- 

 tain heights until they melt in the heat of the low-land sun 

 — all the soil upon the earth, all the sand upon the deserts, 

 all loose material, has been formed. 



Evidencies of glacial action are wide-spread in both Eu- 

 rope and America. Glacial drifts — immense boulders, re- 

 moved a long way from the native rock from which they 

 were separated, often left on the summits of high hills ; peb- 

 bles and cobble-stones, worn by attrition, — the loose drift 

 and soil of glacial moraines, — may be found all through our 

 Northern country. Scratches or grooves made on the sur- 

 faces of the rocks by hard stones caught in the ice, and 

 dragged along by the force of the trend, indicate the direc- 

 tion of the glacier's flow. The region of glacial action may 

 be mapped out with accuracy wherever its effects have been 

 closely studied. The glacial moraines form many of the 

 hills which we now observe in the regions where glaciers 



