CHAP. XVIII. ICE-ACTION IN NORTH AMERICA. 355 



the glacial farrows and stria) imprinted almost everywhere on 

 the solid rocks underlj-ing the drift. Their direction rarely 

 deviates more than fifteen degrees E. or W. of the meridian, 

 so that w^e can scarcely doubt, in spite of the general dearth 

 of marine shells, that icebergs floating in the sea, and often 

 running aground on its rocky bottom, were the instruments 

 by which most of the blocks wei'e conveyed to southern 

 latitudes. 



There are, nevertheless, in the United States, as in Europe, 

 several groups of mountains which have acted as independent 

 centres for the dispersion of erratics, as, for example, the 

 White Mountains, latitude 44° 'N., the highest of which. 

 Mount Washington, I'ises to about 6300 feet above the sea ; 

 and, according to Professor Hitchcock, some of the loftiest 

 of the hills of Massachusetts once sent down their glaciers 

 into the surrounding lower country. 



Great southern Extension of Trains of Erratic Blocks in 

 Berkshire, Massachusetts, U.S., lat. 42° iV". 



Having treated so fully in this volume of the events of the 

 glacial period, I am unwilling to conclude without laying 

 before the reader the evidence displayed in North America, 

 of ice-action in latitudes farther south, by about ten degrees, 

 than any seen on an equal scale in Europe. This extension 

 southwards of glacial phenomena, in regions where there are 

 no snow-covered mountains like the Alps to explain the ex- 

 ception, nor any hills of more than moderate elevation, con- 

 stitutes a feature of the western as compared to the eastern 

 side of the Atlantic, and must be taken into account when we 

 speculate on the causes of the refrigeration of the northern 

 hemisphere during the post-pliocene period. 



In 1852, accompanied by Mr. James Hall, State geologist 

 of New York, author of many able and well-known woi-ks 



