© TAG VALE VIS; 
which the lower terrace lies. He maintains on his own part that the 
evidence of two distinct glacial epochs is insufficient, and holds that 
“the deposits of glacial gravel upon the three-hundred-foot rock shelf 
have been produced partly by an extensive filling up of the Allegheny 
gorge as far as Pittsburg and somewhat below, and lower down by the 
effect of the Cincinnati ice-dam, which set back the water up to this 
level, and is sufficient to account for many of the facts. Under this 
view these high-level deposits would coincide approximately with what 
Dana calls the ‘Champlain epoch,’ during which there was considerable 
depression of land at the north, the influence of which may have been 
felt as far south as the latitude of Pittsburg.” 
The rejection of interglacial erosion, and the introduction of the 
Cincinnati ice-dam as an agency seems to the reviewer to very greatly 
weaken the case. ‘The unfortunate ice-dam hypothesis was originally 
urged as specially applicable to the high-level terraces of the upper 
Ohio and its tributaries; indeed it may be said to have had in them its 
raison @ étre, but investigation has shown that it is altogether untena- 
ble. The author himself has been forced to abandon it for the upper 
region where the phenomena are conspicuous and have been com- 
petently studied. It is safe to say that the same fate will befall it in 
its application to the terraces farther down the river, for they are of 
the same order and have the characters of river terraces and not 
those of ponded-water terraces. Any interpretation hung on the ice- 
dam hypothesis is quite certain to have an early fall. Excluding this, 
it is either necessary to suppose that the valley was eroded to a depth 
of more than 220 feet (either in drift or in rock) before the floods of 
the later glacial epoch formed the lower terraces, or to regard these 
lower terraces as remnants of the high-level filling cut into terrace 
form in later times and more or less re-worked on the surface in the 
process. If the supposed high-level filling really occurred in the time 
of the Champlain depression, to which the author refers it, very much 
the largest part of all the erosion that has taken place since must have 
occurred before the implement-bearing terraces were formed, and, 
accepting the general estimates of post-glacial time favored by the 
author, this might not impossibly bring their formation this side of the 
reign of the Pharaohs. 
But in reality the author assumes that the great interglacial erosion 
took place (though he has not yet come to call it interglacial, and he 
would probably still wish it understood to be a reéxcavation) for he 
