MORAINES OF RECESSION 453 
the best modern example of it." But this glacier is the dump- 
ing ground of hundreds of Alpine glaciers of the most pro- 
nounced type, all descending steep, short slopes from high 
mountains, and carrying heavy loads of débris—superglacial 
loads as medial and marginal moraines, as well as heavy engla- 
cial loads in their bottom layers. Contrasted with this the Lau- 
rentide glacier had no Alpine feeders whatever. Substantially 
all that it accomplished in the transportation and deposition of 
drift was done by its bottom layers in englacial fashion. The 
Malaspina apparently suggests nothing that would controvert 
the general conclusions drawn from other sources. For its most 
characteristic features are exceptional, and obviously do not 
apply to the Laurentide ice-sheet nor to ice-sheets in general.’ 
THE PROBABLE DURATION OF THE PERIODS OF GLACIAL 
OSCILLATION. 
A little examination will show that no short period, such as 
35, 100, or even 300 years will suffice for the building of the 
moraines. From Fort Wayne to Port Huron there are five 
moraines with four intervals of almost exactly fifty miles each. 
These constitute perhaps the simplest group in the whole moraine 
series. They have the widest and most regular intervals and 
some of them, when not too deeply water-laid, are the very best 
types of the structure characterizing deposition at a climax of 
readvance. The intervals are so wide, and the valleys in which 
prove that it was of continental extent. From present indications it would seem 
almost certain that future investigations will establish this as a fact. But even sup- 
posing moraines to be formed sometimes by basal clogging, what could be the cause 
of such widespread periodic clogging if not climate ? 
rMt. St. Elias and its Glaciers,” Am. Jour. Sci., Vol. XLIII, March 1892, pp. 
169-182; ‘‘ Malaspina Glacier,” Jour. GEOL., Vol. I, No. 3, pp. 219-245. 
?Mr. Upham has recently enlarged and elaborated Professor Russell’s suggestion, 
but apparently without throwing any new light on the obscure processes involved. 
(Am. Geol., Vol. XIX, June 1897.) He also endeavors to enforce the Malaspina 
glacier, which is a perfect example of the Piedmont type, as a criterion for interpret- 
ing the Laurentide ice-sheet or continental glacier. In this effort he even goes so far 
as to call the Malaspina glacier an ice-sheet—an application of the term which is 
clearly erroneous and misleading. 
