36 Tlie American Geologist. July, i^yy 
of doubf remains; the barrier was glacier ice, which, as one 
vast sheet, crept slowly forward from the north, impelled bv 
gravity and its own semi-plastic quality to follow the lines of 
least resistance across the country. The moraines of recession 
were made by it and they mark halting places of its retreating 
front. Its solidity and great extent and thickness, as evidenced 
bv the general import of a wide range of glacial phenomena, 
show it to have been fully capable of constituting the retaining 
dam or barrier -of lakes of such magnitudes as those described 
above. The great ice-dams of lakes Maumee, Whittlesey and 
Warren far surpassed all modern examples in the grandeur of 
their proportions, and they were as efifective while they en- 
dured as the land barriers which retain the Great Lakes of to- 
day. The study of the ice-dams and the lake remains associ- 
ated with them is highly important in another way, for, with 
the realitv of the dams established, many new and helpful 
lights are thrown upon the character, conditions and behavior 
of the ice-sheet itself. 
Until two or three years ago, the opponents of the theory of 
ice-dams had the satisfaction of seeing its advocates suffer ap- 
parent failure in every attempt to locate definitely and on actual 
evidence the place of the supposed dams. Mr. Gilbert, behev- 
ing that he had traced the Iroquois beach to its end near 
Adams Center, N. Y., supposed an ice-dam to have rested ai 
that place. Mr. Leverett, having traced the Leipsic beach to 
an apparent end in the city of Cleveland, concluded that an ice- 
dam had stood there on the Newburg moraine. In western 
New York, Mr. Leverett thought that the Crittenden or Forest 
beach ended near Indian Falls and was correlated with an ice- 
dam which stood on the Lockport moraine. Subsequently, 
however, Spencer and Gilbert traced the Iroquois beach be- 
yond Adams Center; Upham traced the Leipsic beach beyond 
the Newburg moraine at Cleveland and Fairchild followed the 
Crittenden beach to Lima, N. Y., east of the Genessee river. 
In a recent paper, Dr. Spencer claims in effect that these 
later extensions of the beaches beyond the supposed places of 
the dams are damaging failures amounting almost to disproof 
of the ice-dam theory.* But even as the facts stood then, 
*"An Account of the Researches Relating to the Great Lakes." 
Am. Geol., vol. XXI, Feb. 1898. pp. 116-117. 
