38 THE POLAK GLACIERS. 



from the slates arid shales, and loam from the softer lime-rocks. 

 But the most striking effects which the polar glacier produced 

 were the long ridges of gravel and bowlder-cla}^ hills which it 

 scraped up as it advanced, and left at the end of its journey, or 

 at each halting-place of its retreat. For it must be borne in mind 

 that the glacier was still pushing southward all the time that it 

 was, on the whole, retreating. These terminal moraines are 

 either the promiscuous gatherings of clay and bowlders and 

 earths of all kinds, or, if they have been subjected to the sorting 

 influence of moving waters, they are gravel hills with sandy 

 bases, and clay flats extending usually to the southward of them. 

 They run in somewhat parallel courses easterly and westerly, 

 sometimes hundreds of miles. Great numbers of these concen- 

 tric ridges may be counted in Western New York, between the 

 long Lake Ontario ridge and the lake hills of the south part of 

 the State. Several cross the New England States, one running 

 along the coast of Maine, and westerly through the White 

 Mountains. In addition to these are the lateral moraines, run- 

 ning, in an opposite direction. These were, some of them, pushed 

 out at the sides by outstretching arms of the glacier ; others were 

 formed by streams running down through breaks or fiords in the 

 melting ice-sheet. So extensive and so marked are the traces of 

 the great polar glacier over all middle latitudes both north and 

 south, that it may truly be called the great landscape-gardener of 

 the temperate zones. 



JBut it is natural to conclude that, if there has been one glacial 

 era caused by astronomical cycles, there must also have been 

 others in earlier geological times. And, as we turn back the 

 pages of the great earth-book, we find therein recorded the evi- 

 dences of the vicissitudes of climate which we thus anticipate; 

 but, if we mistake not, in continually lessening force and extent 

 the further back we go. For long ages previous to the recent 

 glacial epoch, through all the Tertiary era, the fossil plants and 

 animals indicate the prevalence of a warm and genial climate 

 over the greater part of the globe. Then come the chalk-beds 

 of the Cretaceous period, in which are frequently found water- 

 worn blocks of granite and aggregations of pebbles, proving that 



