THE TIME OF THE MAMMOTHS. 161 
be identical with the European representatives) seems on the 
whole to be more ancient than the Mastodon Ohioticus. It 
was beyond all question in existence when the upper terraces 
of our river bottoms were being formed, which must have 
been just as the ice sheet was passing away from the Alle- 
ghanies and was flooding our Western streams with its waters. 
This mastodon on the other hand seems never to be found 
under circumstances which indicate such great antiquity ; it 
seems to have come in after the details of the river courses 
were about complete and all the terraces formed. There can 
be no doubt, however, that these two giants were associated 
during the latter part of their history. Although it is quite 
unusual for two allied animals of very great size to exist to- 
gether in the same field, there is no reason why the Western 
world could not have been broad enough for both. There is 
sufficient difference in the structural features of these two 
races to warrant the supposition that they must have been 
characterized by considerable difference of habit and instinct 
such as would lead them to choose different fields of activity. 
It seems not unlikely, though the evidence is hardly suffi- 
cient to support the assertion, that the mastodon was most 
given to wandering in the swamps, while the elephant ranged 
on higher grounds. 
The Zlephas primigenius, or mammoth, was consider- 
ably taller than the Indian elephants of to-day, though not 
much exceeding them in length. The most striking dif- 
ferences of form were to be found about the head, which 
was considerably higher and more pointed than that of 
the Indian elephant, and provided with tusks, which in- 
stead of projecting downward and forward, curved quite 
abruptly outward and backward. The size of these tusks 
far exceeds those of any living elephant the author has 
measured; tusks-of our North American mammoths have 
been found having a length on the outside of the curve 
of over ten feet, yet wanting both tips and bases. The 
perfect tusk must have been over eleven feet long. In 
AMER. NATURALIST, VOL. IV. 21 
