THE 
AMERICAN GEOLOGIST 
Vol. X. AUGUST, 1892. No. 2 
AN APPROXIMATE INTERGLACIAL CHRONOM- 
ETER. 
N. H. WiNCHELL, Minneapolis. 
Elates iv, v and vi. 
In the present stage of the rapidly unfokUng geolog}' of the 
glacial and succeeding epochs every opportunity to cast light on 
that interesting drama should be improved. The writer contrib- 
utes the following discussion to the subject with a hope that it 
may have some weight in determining one of the questions which 
yet remain unsettled.* The evidence here given that a consider- 
able interval of time, at least equalling that which has elapsed 
since the final withdrawal of the ice from the vicinity of the falls 
of St. Anthony, intervened between the first and second glacial 
epochs, is, perhaps, not conclusive proof, but in the opinion of 
the writer, it is far stronger than any evidence that has been ad- 
duced tending to reduce that interval to a mere recession and re- 
*A prev.oas paper by the writer, The Geology of Hennepin Comity, 1892, 
a chapter ia The History of Minne ipolis, I Atwater, contains the outlines 
of this discussion. 
The duration of interglacial time has also been indicated by Pres. T. 0. 
Chamberlin: Some adiitional eoidences he iring on the intercal between the 
glacial epochx. Bui. Geol. Soc. Am , vol. i, p. 489, 1830. The erosion of 
the trenches to which he alludes, a"; least so far as they lie within the 
drifted latitudes, seems to tmt very doub fully indicate the duration of in- 
terglacial time, since, as urged by James Geikie (On the glacial period 
and the earth movement hypothesis, pp. 18-19) such valle3'S may have 
been eroded in periods long anterior to the first glacial epoch, or even in 
pre-Cretaceous times. 
