INTERPRETATION OF PHENOMENA AS TO VOLUME. 71 
gorge of the Whirlpool rapids was cut out entire by a postglacial stream 
of relatively small volume and is not the site of a preglacial creek gorge, 
as is supposed by many, and this for the following reasons: The element 
of time is a very important factor in gorge-making, especially where the 
circumstances are like those at Niagara. If it were not for the fact that 
the upper hard ledge of limestone resists disintegration stubbornly and 
endures for a long time as an overhanging ledge before it breaks down, 
the cataract would not have time to bore out a deep hole at any place; 
but there appears to have been time enough for deep boring in the mak- 
ing of the Eddy basin, thus demonstrating the solidity and compactness 
of the capping layer of limestone, and this in turn appears to leave us 
no other alternative than to suppose that the gorge of the Whirlpool 
rapids is of postglacial age, provided we assume that the Eddy basin is 
postglacial also. If it should appear, however, that the Eddy basin is 
preglacial, then it is granted that it may be true, so far as can be deduced 
from the study of gorge characters alone, that the gorge of the Whirlpool 
rapids was originally a drift-filled creek gorge of preglacial age. Even 
then, however, the explanation would not be by any means so simple as 
some have assumed, for it would still be necessary to suppose the Eddy 
basin to have been made by a stream of large volume and the gorge of 
the Whirlpool rapids by one of much smaller volume. Hence, while the 
dimensions of the Kddy basin appear to accord better with the Cove sec- 
tion and the Upper Great gorge than with the Saint Davids gorge; while 
the presence of the shoal ledge seems to indicate a difference of age, and 
while the glaciation of the Saint Davids gorge seems to be absent from 
the Eddy basin, none of these evidences, nor all of them put together, 
make a sure case for the postglacial age of this section. The age of the 
Eddy basin, therefore, so far as it can be deduced from the study of 
gorge characters alone, remains a matter of some doubt, but with an ap- 
parent preponderance of evidence inclining to the conclusion that it is 
or postglacial age. 
INTERPRETATION ON EVIDENCE FROM THE UPPER GREAT LAKES 
General statement.—If there were no other way than this of approach- 
ing the study of Niagara history it might never become possible to reach 
a decisive conclusion as to the age and origin of the gorge of the Whirl- 
pool rapids ; but the characters found in the gorge itself are not the only 
available facts. There are others, which have been gathered from out- 
side but closely related areas, that are more impressive and more decisive 
than anything that can be seen in the gorge. It cannot be denied that 
the gorge may have varied its characters in some degree in consequence 
of the action of obscure and undiscoverable causes. Besides, to ordinary 
