Rcsi-arclus rdafuig to the Great Lakes. — Spencer. 1 1 7 
ice dams have been frequently thrown along lines beyond 
which the beaches have subsequently been traced. Thus 
Prof. Claypole* made ice dams in Ontario where open water, 
bounded b}' beaches, was afterwards found to prevail. At 
Adams Centre, Prof. Gilbert drew an ice dam for the Ontario 
basin, beyond which, however, the writer found that the 
old shore line extended, and this was later confirmed by Prof. 
Gilbert. Mr. Leverett made an ice dam at Cleveland, beyond 
which the writer has been informed by two observers that the 
beach extends, and Prof. Gilbert and Mr. Leverett described 
another glacial dam near Crittenden, N. Y., beyond which 
the beaches have been discovered by Prof. Fairchild. x\n- 
other diagnosis of the glacial lakes is the occurrence of gravel 
floors over low divides, which are regarded as the outlets of 
them, and upon this feature alone many such lakes have been 
named. I5ut the advocates of these glacial outlets have not 
■ explained \\o\\ the terraces (at hundreds of feet above the 
drainage) upon the southern side of them are indistinguish- 
able in character from those upon the northern side.f If 
these supposed outlets be evidence per se of glacial dams 
then the most perfect which the writer has ever seen may be 
found within 16° of the equator, at an altitude of less than 
800 feet, suggesting that the Mexican gulf had a glacial dam, 
discharging into the Pacific ocean across the isthmus of Te- 
huantepec — a suggestion which no one would seriously con- 
sider. The writer has also presented the hydrostatic objec- 
tionsj to the impossible long continuance of some of the sup- 
posed dams, the location of which deuiands their drainage 
across ice itself, which would soon be penetrated by the 
warmer waters so as to reduce their level. By straightening 
out the deformation recorded in the deserted shore-lines, 
some of the beaches are shown to have undoubtedly been 
formed at sea-level. § While recent surveys report the dis- 
coverv of additional glacial lakes, or the splitting up of those 
* Report of the meeting Am. Assoc. Adv. Sci. Science, Sept., 1895, 
p. 222. 
t Channels over divides not evidence per se of glacial dams. J. W. 
Spencer. Bull. Geol. Soc. Am., vol. Ill, 1891, p. 491. 
JPost-Plioccne continental subsidence versus ice-dams, hy J. W. 
."Spencer. Bull. Geol. Soc. Am., vol. II, pp. 465-476, 1890. 
§The Iroquois Beach, etc., cited before; and. Deformation of the 
Iroquois Beach, cited elsewhere. 
