EVOLUTION OF ELEPHANTS 371 



Some of these four-tuskers, impelled by hunger or thirst, 

 probably ventured too far on quicksands and became en- 

 gulfed, while others in traversing boggy ground became 

 mired. In these cases, the skeletons are apt to be complete 

 and the bones without scars or blemishes. A few perished 

 on dry ground and became buried by wind-borne dust and 

 sand, but the great majority died on the uplands where 

 their skeletons weathered to pieces and are lost forever. 



Beds containing the remains of these animals are found 

 from Wyoming to northeastern Nebraska. After a long 

 period of time a series of beds, several hundred feet in 

 thickness, were deposited, and through out these occur the 

 scattered remains of elephants and associated animals. Oc- 

 casionally there are actual bone heaps and bone beds. It 

 is apparent then that wherever the overlying material is 

 swept away by wind or water, bones are apt to be laid bare 

 on the surface. Nebraska has been the favourite collecting 

 ground for all of the educational institutions of America 

 and even of Europe. 



The degree of preservation varies widely, but in general 

 elephant bones found in the older beds tend to be hard and 

 enduring, while those of the later beds are apt to be weak 

 and perishable. In the older beds sufficient time has lapsed 

 for the infiltration of mineral salts to give stoniness to the 

 bone, while in the more recent beds there has not been time 

 for this process. 



METHODS OF COLLECTING 



In hunting for the ancient tuskers, the pick and shovel 

 are substituted for the gun, and the sport is not as dry as 

 fossil bones may indicate. Scattered fragments of bone 

 on a talus slope constitute a "lead" which is carefully fol- 

 lowed to its source, and here the work of excavation begins. 

 As soon as the rocky matrix is removed from a few square 



