by modification of food and body structures. Thus 

 these rapidly changing conditions forced an accelerated 

 and diversified development of the mammals. 



Evidence of these changes in America are numer- 

 ous. The tragedies revealed in the investigations of the 

 pitch lakes at Rancho LaBrea in southern California, 

 in which the skeletal remains of the Saber-toothed 

 Tiger and hundreds of other forms no longer existent 

 have been found, and the discovery of fossil Dinosaurs 

 in Wyoming, are indubitable records of these Geologi- 

 cal and attendant climatic transitions. 



We have reason to believe that, millions of years 

 ago, the region between the Allegheny and Rocky 

 Mountains was the bed of a gigantic ocean which later 

 shifted its basin, leaving in its wake, a series of lakes, 

 ponds, streams and swamps, many of which were later 

 drained or dried up. The available land areas were 

 immediately claimed by a luxurious growth of vegeta- 

 tion with which there became associated an interesting 

 fauna. The fossil remains of the plants and animals 

 of that time indicate that the climate was of a tropical 

 or subtropical character. 



Far in the North the long winters were producing 

 quantities of snow and ice which the comparatively 

 short summers could not melt. The accumulated mass 

 grew to gigantic proportions and later covered the 

 whole northern part of this continent. Then this great 

 ice sheet began to move southward. Naturally, as it 

 descended, it brought about a very pronounced change 

 in temperature. This ice sheet, or glacier, which prob- 

 ably attained a height of two miles in some places 

 moved across the northern part of New York and the 

 northern and northwestern part of Pennsylvania, its 



-•i^ 18 >«■- 



