Author's Catalogue. 195 
WHITFIELD, R. P. 
Notice of six new species of Unios from the Laramie Group. 
(Bull. Am. Mus. Nat. His., vol. 19, pp. 483-487, 1903.) 
WHITFIELD, R. P. 
Observations on a Remarkable Specimen of Halysites and De- 
scription of a New Species of the Genus. (Bull. Am. Mus. Nat. His. 
vol. 19, -pp- 489-430, 1903.) 
WILLISTON, S. W. 
North American Plesiosaurs. (Field Col. Mus. Pub. 73, vol. 2, 
No. 1, pp. 76, pis. 29, April, 1903.) 
WRIGHT, G. F. 
The Revision of Geological Time. (Bibliotheca Sacra, vol. 73, 
pp. 578-582, July, 1903.) 
CORRESPONDENCE. 
"How long ago was America peopled." American Geologist, vol. 
xxxii, p. 128. Taking this as his text Mr. Marsden Manson calls at- 
tention to the need of considering the latitude of a place when deter- 
mining the number of years since which any given region has been 
relieved of its load of glacial ice. His remarks relate chiefly to the 
west coast of North America in which he finds the disappearance of 
the glacial ice to vary from 50,000 years in the peninsula of Lower Cal- 
ifornia to 1500 in Alaska — a wide difference surely. Without going 
into his argument, which will be found detailed in the August number 
of the Geologist, one may revert to his citation from professor Upham 
on the probable lapse of time since this continent has been occupied by 
man. Of the various estimates made by different writers of the time 
when the Ice age came to a close he says "Their average of about 
8000 years may be confidently accepted as near the truth" 
That this is a modest demand is clear from the result of the study 
of this period in Europe, and is not without support in this region. 
Here in eastern Canada we arc in the latitude of 45 N, a median 
position on this coast as regard the great ice sheet of the glacial time, 
or perhaps nearer its southern border, yet there are indications that a 
long time has elapsed since the burden of ice was removed from this 
region. 
In the peat bogs that cover extensive tracts along these coasts there 
is a continuous history extending over many years. They have not 
been exploited like those of northern Europe, yet they reveal to us 
some data of general as well as local interest. One small valley on the 
borders of the city of St. John is occupied by a deposit of this kind 
which is now mostly in the condition of forest; yet it has passed 
through the various stages of beaver pond, marsh, peat bog. forest bog, 
peat bog, forest bog, and is now returning to the Condition of 
