360 The American GeologlHt. D.-cfmber, i892: 
drift which fell looacly on the surface from an eiighicial or super- 
glacial position when the ice disappeared. 
Comparison wrnr Termfnal Moraines, Ka.mes, and Kskers. 
Mj' study of the glacial lake Agassiz, under the direction of 
Prof. T. C. (Mianil)erlin, for the United States (leological Sui'vey 
and partly for that of Canada, shows that several large terminal 
moraines, niarking pauses or re-advances interrupting the general 
glacial recession, were accumulated contemporaneous!}' with the 
existence of that lake, while yet the whole duration of Lake Ag- 
assiz was apparently only about a thousand years.* The rapidity 
of formation of the moraines was thus similar with that of the- 
drumlins, and both seem to have l)een made possible only b}" the 
large amount of the englacial drift. The fast retreat of the ice 
indicates that probably its melting border then had usually a more 
steeply sloping surface than in its time of greatest extent to the 
south, and that consequently the rate of motion of the outer part 
of the ice-sheet was commonlj- increased during its final melting. 
Any pause of the retreat for even a few years would therefore 
form a moraine, though the outer belt of the ice may have been 
generally too steep to expose much superglacial drift. But dur- 
ing some stages of the recession we may conclude that consider- 
able tracts of the ice-border were so thinned by ablation that 
much englacial drift became superglacial, with the result that 
when again a colder climate brought a temporary thickening of 
this marginal ice the previously superglacial stratum of drift was 
chiefly amassed in drumlins. The known drumlin areas of New 
Brunswick and New England, New York, Wisconsin, and Mani- 
toba, would therefore be expected to belong to the same stages of 
the closing part of the Tee age. This would imply what seems 
from other reasons not improbable, that the outermost moraines 
in the states east of Ohio and on the east side of the driftless 
area in Wisconsin correspond to some of the inner and late mo- 
raines in the greater part of the region of the Laurentian lakes 
and the upper Mississippi, as perhaps the exceptionally massive 
Leaf hills, Itasca, and Mesabi moraines, which are the ninth. 
tenth, and eleventh of the series in Minnesota. 
*Geol. and Nat. Hist. Survey of Canada, Annual Report, new series, 
vol. IV, for 1888-89, pp. 50, 51 E. Am. Geologist, vol. vii. pp. 224-6,.. 
April, 1891. 
