Rhythmic Accumulation of Moraines. — Uphani. 411 
outlet and the northern will be diminished in volume, or per- 
haps entirely abandoned. 
In this connection it is of interest to consider the relations 
and time of duration of the two outlets of Brule lake. Twen- 
ty miles to the south of this lake are the ancient beaches on 
the north shore of lake Superior, the highest of which has been 
stated to have a northeasterly elevation averaging seven inch- 
es to the mile.* This same elevation at Brule lake, which is 
about eight miles long in an east and west direction, would cause 
the water at the western end to stand over three feet higher than 
formerly — an amount more than adequate to cause an overflow 
at that extremity of the lake. From the drowned character of 
the St. Louis River valley at the western end of lake Superior 
it is clear that that end of the lake has been relatively low- 
ered several feet since the present outlet at Sault Ste. Marie 
was established, and it certainly seems probable that this 
differential elevation is still in progress. j- From the foregoing- 
it may be reasonably assumed that Brule lake, shortly after the 
departure of the ice-sheet from this region, had but one outlet 
and that toward the east; that later elevation of the eastern 
end of the lake caused a part of the water to overflow a de- , 
pression in the western rim of the basin ; that continued dif- 
ferential elevation brought this outlet into equal prominence 
with the first; and that the continuance of this process will 
cause the first outlet to be abandoned entirely, thus making 
a marked change in a minor drainage feature of this part of 
Minnesota. 
RHYTHMIC ACCUMULATION OF MORAINES BY 
WANING ICE-SHEETS. 
l}y Warren Upha.m, St. Paul, Minn. 
North American and European Series of Marginal 
Moraines. 
Definite marginal accumulations of drift are absent or very 
rare on the extreme boundaries of the great ice-sheets which 
in the Glacial period enveloped the northern half of North 
America and northwestern Europe. The margin of the drift 
* Wanen Upham. Geol. and Nat. Hist. Survev of Miun., 2.3tl Ann. 
Rep., p. 164, 1895. 
tCf. Warren Upham. Op. cil... p. 171. 
