REPORT ON FORESTS. 199 



that there were no such extremes of climate between the poles 

 and the equator as prevail to-day. The temperature of the 

 earth's surface had been more or less uniform during the respect- 

 ive periods, as evidenced by the fact that rocks of the same age 

 the world over, wherever they have been examined, contain the 

 remains of vegetation which are identical generically and even 

 specifically to a large extent. 



The elevation which began in the Tertiary period, however, 

 caused, or at least was coincident with, the greatest changes, 

 climatic and biologic, which are anywhere recorded in geologic 

 history. The climate became gradually more and more severe 

 at the north and finally culminated in what we have come to 

 call the Ice Age or Glacial Epoch of the Quaternary period. 



The change must have been a gradual one, extending over a 

 long period of time, as we are justified in concluding from the 

 fact that the vegetation which was in existence at the time when 

 it was finally overwhelmed by the accumulation of ice and snow, 

 which extended southward in New Jersey as far as Perth Amboy 

 in the east and Belvidere in the west, was identical in all respects 

 with that of to-day. In other words, the flora of the Tertiary period 

 had had opportunity to become modified by the changing con- 

 ditions before its final extermination by the ice sheet, which im- 

 plies a long period of time. Every species thus far discovered 

 in the bowlder till, in the glacial sands or gravels, or in buried 

 swamp deposits, is identical with some Jiving species. Some of 

 the Tertiary species were able to continue their existence by 

 migrating southward, and these are in existence to-day, but such 

 as were unable to migrate from the area of glaciation were abso- 

 lutely exterminated and only such species as were able to exist 

 under the changed conditions southward were able to re-establish 

 themselves after the final recession of the ice. I do not know of 

 remains of the vegetation of this period having been found in 

 New Jersey, and such as have been found elsewhere are scanty 

 in amount, but all the species identified are the same as those 

 now living. 



CONCLUDING REMARKS. 



The final recession of the ice was accompanied by a sub- 

 sidence of the land and a consequent restriction in its area. 

 The shore-line advanced inland, and in places only the more 



