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180 IOA¥A ACADEMY OP SCIENCE 
this delicately fragile sheath could have survived the mechanical attri- 
tion which necessarily would have attended its removal by glacial ice 
and swollen streams to the place where it was found. The horny part 
of the claw decays rapidly. Bears’ claws buried with Indians which 
inhabited Iowa since the coming of the white man have this horny part 
completely decayed. It is safe, therefore, to infer that if our Mylodon 
were preglacial, the claw proper would hav disappeared by natural 
process of decay long before the advent of the pre-Kansan ice, and we 
should have to believe that the specimen, in essentially its present con- 
dition, had been transported by at least two energetic and none too 
gentle agents without injury to the fragile sheath. Even if the gla- 
ciers had treated the specimen ever so tenderly, a very short journey 
in gravel laden streams would have obliterated every vestige of the 
very vascular bone that covered the root of the horny claw. In this 
case, as in most of the others, a pre-glacial age for the animals repre- 
sented by the fossil bones is simply unthinkable. 
Another point must not be overlooked. If the fossils under consid- 
eration had been incorporated in the pre-Kansan drift as would certain- 
ly have been the case with many of them if they are of preglacial age, 
the larger pieces could never have found their way into the Aftonian 
gravels retaining amdhing like their present state of perfection. A 
large bone or an entire tusk would not be washed out of the tough 
glacial clays all at once. An end or a side would be exposed long before 
the whole specimen could be completely freed and this, affected by ■ 
corrasion and weathering, would crumble into small fragments; the 
process of waste would keep pace with the rate of removal of the cov- 
ering till, little, if anything, would be left to be transported and de- 
posited by Aftonian streams. But there is no need of multiplying 
arguments; the improbability of these fossils being pre- Aftonian will 
be recognized and acknowledged by any one who has seen the material 
and knows the conditions under which it was found. 
