CHAP. XVIII. GLACIAL PERIOD IN NORTH AMERICA. 351 



CHAPTER XVin. 



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 DE- 

 SCRIPTION OF THEIR LINEAR ARRANGEMENT AND POINTS OF DEPART- 

 URE THEIR TRANSPORTATION REFERRED TO FLOATING AND COAST ICB 



GENERAL REMARKS ON THE CAUSES OF FORMER CHANGES OF CLI- 

 MATE 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 OPPO- 

 SITE SIDES OF THE ATLANTIC IN THE GLACIAL PERIOD NOT STRICTLY 



SIMULTANEOUS NUMBER OF SPECIES OF PLANTS AND ANIMALS COMMON 



TO PRE-GLACIAL AND POST-GLACIAL TIMES. 



rVN the North American Continent, between the arctic 

 ^ circle and the 42d 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 con- 

 tinued 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 proboscidian 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 



