THE REIGN OF ICE. 219 



mowing down the forests, crushing tree-trunks, or burying 

 them, with the rubbish of the rocks, from ten to sixty feet 

 beneath the surface. Such buried tree-trunks have thus 

 lain to the present day, and we frequently encounter them 

 in deep excavations for wells, though my friend Professor 

 Lesquereux has strangely asserted the contrary. With 

 other relics of the vegetation of the ancient world were 

 necessarily buried the seeds and fruits of the species then 

 in existence, a fact of which I shall find the use hereafter, 

 in speaking of prairies. 



The great glacier moved onward, unheeding equally 

 rocky knob, and swelling hill, and river gorge. I have 

 stated that from the close of the Carboniferous Age the 

 Northern States were dry land. Rains fell, as now, upon 

 the surface, and nourished the vegetation which had found 

 a foothold. The surplus waters gathered themselves, as 

 now, into streamlets large and small, and these, on their 

 way to the sea, wore river-channels in the surface rocks. 

 Across these rivers, across these gorges, the great glacier 

 strode, ignorant of the obstacles to its movement. It 

 bridged Niagara River, it bridged Long Island Sound, 

 and bathed itself in the mild waters of the ocean beyond. 

 It obliterated river-channels, and dug out new ones. It 

 plowed anew the country marked off by the feebler agen- 

 cies of the preceding epoch. It made a tabula rasa, and 

 outlined after a different pattern the topographical and 

 hydrographical features of the Northern States. Many an 

 ancient river-channel has been brought to light by railroad 

 excavations, and more especially by the borings for petro- 

 leum that have taken place within the last few years. In 

 many instances the general rocky structure of a region has 

 determined the location of the streams through the same- 

 valleys as before the work of the glacier ; but even here 

 we find the position slightly varied, and in nearly all cases 



