178 The American Geoloqint. March, iwo 
ternary lakes. Its area is roughly estimated at 1 50, 00(1 square 
miles.* 
Tin- Pleistocene historij of nortlieicUrrn louui. B}' W J Mc(jEE. 
This paper was a partial resume of the author's memoir of this 
title in the Eleventh Annual Report of the U. S. Geological Sur- 
vey, now in press. Two incursions of ice from the north have 
each spread a drift sheet upon this district, and in each case only 
little of the drift can be ascribed to a local origin. Probably 95 
per cent, of both the earlier and later till and of the associated 
stratified deposits came from areas north of Iowa. Boulders of 
small size, comprising many of hornblende schist characterize the 
lower and older till, while the upper till has man}' large boulders 
of granitoid and gneissic rocks, usually occurring of all sizes up 
to 15 feet in diameter. Often much larger l)Oulders are found, 
and one was mentioned having a diameter of 47 feet. 
A very remarkable feature of the early glaciation of this dis- 
trict is the absence of glacial stria?, except in one isolated locality, 
on the bed rocks of a drift-covered country about 16,000 square 
miles in area. Not all of the preglacial residuar}' clay was re- 
moved, and no glacial erosion of the underlying rocks took place. 
Between the first and second ice incursions forests grew on this 
area and their remains form a forest bed of abundant logs and 
branches, with occasional peat accumulations, encountered b}' 
nearly every well of whole townships and traceable over several 
counties, lying between the lower and the upper till. 
The eastern part of the district is covered with loess, and the 
western border of the loess has a descent like a terrace 10 to 20 
feet or more, to the surface of the sheet of till which stretches 
thence westward upon the tract that was covered by the Minne- 
sota and Iowa lobe of the ice-sheet while the loess was being de- 
posited. Upon the till area loess occurs here and there forming 
ridges much higher than the surrounding land. These ridges 
named pdha, trend in parallelism with the movement of the ice- 
*A different view, which regards lake Warren as a glacial lake, held 
by the barrier of the retreating ice-sheet on its nortlieast side and at- 
taining at its maximum stage probably only about half as great area 
as supposed by Dr. Lawsoii, is stated by G. K. Gilbert in "History of 
the Niagara IJiver." Sixth Annual Keport of the Commissioners of the 
State Reservation at Niagara, for J8S9. pp 61-84, with three maps 
(also in the Smithsonian Keport for 1890), and by Warren Upham in 
Bulletin of the Geological Society of America, vol. ii, pp. 258-265, and 
vol. III. ])p. 484-487. 
