THE AFTONIAN AGE OF THE AFTONIAN MAMMALIAN FAUNA 
BY SAMUEL CALVIN. 
The publication of the paper on the Aftonian Mammalian Fauna, in 
the Bulletin of the Geological Society of America, volume XX, pages 
341-356, has very naturally elicited a number of questions Avhieh, how- 
ever, bear chieflj^ on two points : First, are we certain as to the pre- 
cise age bf the gravels? and, second, are we certain that the mammal- 
ian remains described may not be older than the Aftonian? Two papers 
prepared by Professor Shimek and_ published in the Bulletin of the 
Geological Society of America, volumes XX and XXI set out the evi- 
dence bearing on the first of the questions; it nvill be sufficient here to' 
Consider the second. The first mammalian bones which came into my 
hands from the Aftonian were few in number and small in size. As to 
age there were just two possibilities, as there are but two with respect 
to any and all the fossil remains found in the gravels. The animals 
represented were either contemporary with the deposition of the gravels 
— or practically so — or they lived in preglacial time. They certainly 
did not live during the interval of pre-Kansan glaciation. The bones 
that first came to hand were assumed to be preglacial because that 
seemed best to accord with the state of knowledge at the time relative 
to the age and genesis of the gravels. On that assumption their his- 
tory could be easily sketched. They had been imbedded and preserved 
in some preglacial deposit; they had been separated from the original 
deposit by washing or weathering, or the gouging action of glacial ice ; 
they had been picked up by the pre-Kansan glaciers and incorporated 
in the sub-Aftonian drift ; they had been washed out of the drift in 
Aftonian time and carried bj^- Aftonian streams to be eventually laid 
down as part of the assorted Aftonian gravel. This assumption tallied 
very well with what certainly was the history of a number of other 
fossils taken at the same time from the gravels. These include parts of 
the dentary bone with broken teeth of Clidastes, two fragments of 
guards of belemnites, and an internal cast of one of the air chambers 
of Placenticeras, all from Upper Cretaceous horizons; there is also a 
left valve of a narrow Gryphaea which may be Jurassic*; and there is a 
fragment of a corallum of Favosites from the Niagara. 
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