Boston Meeting of the Geological Society. -1'.' 
great erosion which occurred between the depositions of the two or 
more systems of glacial gravel. Pour hypotheses relative to the history 
of the phenomena were introduced, three of which postulate but a 
single interglacial epoch, and one of which postulates two interglacial 
epochs. Computed ratios of work done in each of the stages of tilling 
and of excavation under each of the several hypotheses were presented. 
The amount of valley rilling associated with the terminal moraines (i. e. 
the valley rilling of the last glacial epoch) was taken as the unit of com- 
parison for valley filling, and the amount of postglacial excavation of 
the gravels was taken as the unit of excavation. The amount of valley 
rilling of the earlier glacial epoch under the four hypotheses ranged 
from two and two-thirds to seven times that of the last glacial epoch. 
The amount of valley excavation in the interglacial epoch under each of 
the three hypotheses which postulated one such epoch was thirteen 
times the postglacial excavation; in the remaining hypothesis it ex- 
ceeded thirteen times by an undetermined amount. Attention was di- 
rected to the fact that, to the extent to which we assume preglacial 
excavation of the Allegheny gorge, to that extent we magnify the valley 
filling of the early glacial epoch. The import of all these hypotheses is 
alike on most of the vital points relative to the history of the region. 
They all greatly emphasize the importance and significance of the first 
glacial epoch. They all show very important intervening excavation, 
when compared with the erosion which has taken place since the Gla- 
cial period. They all indicate that, while the last great glacial invasion 
was very much more pronounced in its apparent effect, and in the ex- 
pression which it took on, it was after all but a small factor of the total 
accomplishment of the Glacial period. 
Prof. I. C. White, in discussion of this paper, thought that no suffi- 
cient evidence is adduced for any of these lines of northerly drainage 
from the upper Ohio basin. He is familiar with nearly the whole area, 
and thinks that the high rocky rim facing lake Erie is continuous. He 
had not been able to find any interruption in it sufficient to furnish a 
channel for the supposed outlet. Besides, he had found, while con- 
ducting the survey of the region in the Susquehanna valley near the 
terminal moraine, that there is the same northerly descent of the bed 
of that river north of the moraine, but no one supposes that the Sus- 
quehanna ever ran to the north from that line. His conclusion, there- 
fore, was that the differential depression to the north was a consequence 
of the Champlain subsidence, from which the land has only partially 
recovered. He was inclined also to believe that the weight of the 
glacial debris accumulated in exceptional amount over the belt imme- 
diately north of the moraine is a partial explanation of the remaining 
northerly depression. 
Prof. G. F. Wright suggested that, in the recession of the waterfalls 
which doubtless characterized the region during the formation of the 
rock gorge, the beds of the streams may have been eroded to very un- 
equal depths, as is the case now below Niagara, where in the gorge the 
rock bottom is 200 feet or more below the general surface, while from 
Lewiston to lake Ontario there can be no such depth. He cited a simi- 
lar instance in Snake river, Idaho, just above Shoshone falls, where the 
depth of the river below the general level suddenly increases from a few 
feet to 100 feet or more. 
* .*)?. Glacial History of western Pennsylvania. (!. Frederick 
Wright, Oberlin, Ohio. The author presented the facts observed near 
Warren, Pa., by Mr. L.everett and himself in company, which show that 
the rock bottom in the valleys of the Allegheny and its tributaries at 
that point was nearly at the same depth before the earliest ice invasion 
as now. A continuous bank of clearly stratified gravel containing 
granite nebblee rises from the Hood-plain of the Oonewango to the level 
of the 250 feet rock shelf, which was part of the river bed in biter 'Per- 
