CHAP. xvm. GLACIAL PERIOD IN NORTH AMERICA. 35T 



CHAPTER XVIII. 



THE GLACIAL PERIOD IN NORTH AMERICA. 



POST-GLACIAL STRATA CONTAINING REMAINS OF MASTODON GIGANTEUS 



IN NORTH AMERICA SCARCITY OF MARINE SHELLS IN GLACIAL DRIFT 



OF CANADA AND THE UNITED STATES GREATER SOUTHERN EXTENSION 



OF ICE-ACTION IN NORTH AMERICA THAN IN EUROPE TRAINS OF 



ERRATIC BLOCKS OF VAST SIZE IN BERKSHIRE, MASSACHUSETTS 



DESCRIPTION OF THEIR LINEAR ARRANGEMENT AND POINTS OF DE 

 PARTURE THEIR TRANSPORTATION REFERRED TO FLOATING AND 



COAST ICE GENERAL REMARKS ON THE CAUSES OF FORMER CHANGES 



OF CLIMATE AT SUCCESSIVE GEOLOGICAL EPOCHS SUPPOSED EFFECTS 



OF THE DIVERSION OF THE GULF STREAM IN A NORTHERLY INSTEAD 



OF NORTH-EASTERLY DIRECTION DEVELOPMENT OF EXTREME COLD 



ON THE OPPOSITE SIDES OF THE ATLANTIC LN THE GLACIAL PERIOD 

 NOT STRICTLY SIMULTANEOUS NUMBER OF SPECIES OF PLANTS AND 

 ANIMALS COMMON TO PRE-GLACIAL AND POST-GLACIAL TIMES. 



ON the North American Continent, between the arctic 

 circle and the 42nd parallel of latitude, we meet with 

 signs of ice-action on a scale as grand if not grander than in 

 Europe ; and there also the excess of cold appears to have been 

 first felt, at the close of the tertiary, and to have continued 

 throughout a large portion of the post-pliocene period. 



The general absence of organic remains in the North 

 American glacial formation, makes it as difficult as in Europe, 

 to determine what mammalia lived on the continent at the 

 time of the most intense refrigeration, or when extensive 

 areas were becoming strewed over with glacial drift and 

 erratic blocks, but it is certain that a large proboscidean now 

 extinct, the Mastodon giganteus Cuv., together with many 

 other quadrupeds, some of them now living and others 

 extinct, played a conspicuous part in the post-glacial era. 

 By its frequency as a fossil species, this pachyderm represents 



