MARYLAND GEOLOGICAL SURVEY 161 



variable that little dependence can be placed upon them alone for pur- 

 poses of slight specific differentiation. Specimens in the TJ. S. National 

 Museum from one horizon and one locality at Afton, Indian Territory, 

 show that the last molar may have four cross ridges, five cross ridges, or 

 five cross ridges and a heel. 



In its low, massive build, shape of the skull and character of the teeth 

 the mastodon differs so entirely from the mammoth that the two may be 

 told apart by the most casual observer. The tusks even differ in some 

 respects from those of Elephas by being shorter and stouter, though 

 these differences are more marked in males than in females, the tusks 

 of the latter being slender for their length. The tusk of a full-grown 

 male mastodon is from 8-J to 9^ feet long and 7 to 8 inches in diameter, 

 while the tusk of a male mammoth is from 9 to 11 feet long and 6 to 7 

 inches through. 



In the eastern United States the mastodon seems to have existed to a 

 much later date than the mammoth, having entered New York after the 

 retreat of the ice sheet and remained there during the formation of the 

 peat beds and the filling of the valleys and small streams to the west of 

 the Catskills. The freshness of some of the bones renders it possible 

 that the mastodon was contemporary with early man, but while the writer 

 firmly believes this to be true he is at present unacquainted with any 

 positive evidence that such was the case. 



The size of the animal has been popularly very much over-estimated 

 and this erroneous idea has been encouraged by equally erroneous figures 

 and mounted specimens. The skeleton of an old male from Newburgh, 

 N. Y., in the Museum of the Brooklyn Institute, which is a good rep- 

 resentative animal, measures 9 feet 4| inches to the top of the backbone, 

 and the equally adult female from Michigan in the IT. S. National Mu- 

 seum stands 7 feet 8 inches in height. Allowing for flesh and skin it is 

 safe to say that the average full-sized mastodon was under 10 feet in 

 height or about the size of the Asiatic elephant, although much more 

 heavily built. 



Occurrence. — This species, as represented by its fossil remains, is by 

 far the most abundant and most widely distributed of any species of 

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