80 The American Geologist. Auguf^t, 1892 
comuieuoement of the interglucitil falls of St. Anthony, is distant 
from the mouth of Bassett's creek where they stopped their reces- 
sion, twelve and a half miles, or about 50 per cent, further than 
the distance through which the post-glacial falls have receded, 
from Fort Snelling to Minneapolis. Taking the results of the 
calculation of the post-glacial recession as a measure of intergla- 
cial recession, we find they compare with the interglacial condi- 
tions as follows: 
Po«t-gJ(tcial recession 8^ miles, in 7,800 yearn. 
Iitterglaeitil recession^ 12|^ miles, nt a rate perhaps 25 per ceni. 
/aster. 
The greater distance will more than compensate for the greater 
rate, and will allow us to add to the time required about 25 per 
cent, of the post-glacial time. This indicates 9,750 years for the 
lapse of time required for interglacial recession. 
Such an interval of time, if it occurred between the two glacial 
epochs, would allow for something more than the temporary re- 
treat and re-advance of the same ice sheet. It would give time 
for the weathering of the till of the first glacial epoch and the 
excavation of valleys in it by interglacial streams. It is time 
sufficient for the growth of forests and the accumulation of peats, 
for the development of a somewhat characteristic fauna and flora, 
and for the establishment of some human habitation as well as 
civilization. The whole Egyptian dynasty, and perhaps the dawn 
of the Chinese, might be compassed in such a period. 
NOTES ON MANGANESE IN CANADA. 
n. p. BiiuMELL, Ottawa. 
Assistant, Division of Mineral Statistics and Mines Geological Survey 
of Canada. 
(Communicated by permission of the Director.) 
In prei)aring the following brief sketch of the various impor- 
tant deposits of manganese in Canada, 1 have embodied the 
greater part of tue article on that substance which I prepared for 
the annual report of the division of Mineral Statistics and Mines 
for 1890.* 
That the industry has not attained greater commercial [jromi- 
nence is due rather to its distance from market than to any in- 
sufficiency of supply; this applies, however, more especially to 
*Annual Report Geol. Surv., part S, Vol. v, 1889-90. 
