Pleistocene Papers. Ottmra Meeting of G. S. A. 171 
It comes from one of the lowest beds of the Cleveland shale, a 
horizon which has thus far yielded only an as yet nndescribed 
species of Titanichthys. 
Some other fragments are also in the hands of Dr. Clark but 
cannot at present be described. The chief of them is a much 
broken plate, apparently dorso-medial, which corresponds in 
size to what would be expected, being about three times as large 
as the similar plate of C. decipiens. These, however, must await 
further discoveries. 
PLEISTOCENE PAPERS READ AT THE OTTAWA 
MEETING OF THE GEOLOGICAL SOCIETY 
OF AMERICA. 
Among the papers read and discussed at the recent meeting of 
the Greological Society of America in Ottawa, Canada, December 
28, 29, and 30, 1892, the following related to the glacial drift 
and history of the Pleistocene period. 
Distinct glacial (qwchs, and the criteria for their recognition. 
By R. D. Salisbury. The question concerning how much de- 
crease and ensuing re-advance of ice-sheets should constitute an 
interglacial epoch is to be answered by {a) the distance of the 
glacial recession, {h) the length or shortness of the time between 
successive advances of the ice, (r) climatic changes in the area of 
the oscillations, and {d) intervening geologic changes or move- 
ments of uplift or depression of the land. 
The criteria for discrimination of ice invasions so distinct as to 
be properly called separate epochs were considered under the fol- 
lowing heads: 
1. Forest beds intercalated between deposits of till. These do 
not necessarily indicate truly interglacial conditions, but are to 
•be so interpreted if their species belong to a temperate climate or 
to one as warm as now in the same locality, also if they have a 
great geographic extent. 
2. Bones of land animals fossil in strata with till beneath and 
above. 
3. Lacustrine or marine fossiliferous beds underlain and over- 
lain by till, if they denote a climate as temperate or mild as 
now. 
