OTHER INTERPRETATIONS OF THE PHHNOMENA. 81 
Dr Spencer also supposed a period of discharge for the upper lakes 
through a strait by way of the Mattawa valley, but he placed it earlier 
in Niagara history, during the recession from Lewiston to Fosters flat, 
and hence did not correlate it with the gorge of the Whirlpool rapids. 
Indeed, he postulates a concentration of full volume with a fall of 420 
feet while this section of the gorge was being made. He recognized the 
narrowness of the gorge of the Whirlpool rapids, but he supposes it to 
be as deep as any other part of the gorge. 
The first attempt to account for the several features of the Niagara 
gorge in a somewhat detailed manner was that of Julius Pchlman, of 
Buffalo, New York, who read a paper on this subject before the American 
Association for the Advancement of Science at its meeting in that city 
in August, 1886.§ While Dr Pohlman’s paper cannot be accepted today 
as a true analysis of the gorge history, it was nevertheless a very credit- 
able effort, considering the fact that it was a pioneer attempt and that 
next to nothing was then known of the postglacial history of the upper 
lakes. Dr Pohlman supposed that the “ preglacial Tonawanda” creek 
had cut a gorge from the escarpment at Saint Davids back through the 
Whirlpool and nearly up to the American fall, and that other small 
streams had cut out ravines where the modern gorge now lies, between 
the Whirlpool and Lewiston. He thus reduced the work of the post- 
glacial river to a minimum, and supposed its entire duration, and hence 
the duration of postglacial time also, to have been only about 3,500 years. 
Others now following the same general idea conceive the preglacial gorge 
to have extended only to the upper end of the gorge of the Whirlpool 
rapids, and they put the duration of the river at from, 5,000 or 7,000 to 
the Whirlpool rapids is not disproved.”” However, when the abstract of the present paper was read 
at Detroit, Mr Gilbert expressed himself in discussion as favoring the correlation suggestion. 
Messrs Wright, Spencer, and Claypole favored the view of Pohlman, or a slight modification of it. 
It is interesting to compare Mr Gilbert’s original hypotheses with what we now know of the lake 
history. In his ‘‘ History of the Niagara river” he presented two maps showing hypothetical stages 
or episodes of the Great lakes. In plate iv Nipissing Great lake as now defined is partly antici- 
pated, while in plate v one episode of lake Algonquin, that with the Trent Valley outlet is shown. 
Plate v, however, is merely a modification of Spencer’s earlier hypothesis to fit glacial theory. 
Other more important episodes of the latter lalke when it discharged southward are now recognized, 
but the data for unravelling their complex history had not then been collected. In plate iv the 
river discharging the upper three lakes is shown as passing down the Mattawa and Ottawa valleys 
to Montreal, and that discharging the lower two lakes follows the course of the present Saint Law- 
rence to the same place, showing apparently that Mr Gilbert did not correlate the marine Cham- 
plain submergence in the east with this episode of the lakes. In reality, the sea at that time entered 
the Ontario basin and reached far up the Ottawa valley (compare Mr Gilbert’s plate iv with map 
no. 4in “A short history of the Great lakes’’). Mr Gilbert indicates much more land tilting than 
has been found to exist, and his shorelines are consequently made to dip under the present lakes 
toward the southwest much sooner than they do in reality. Nevertheless, his two hypothetical 
episodes have been verified to a remarkable degree. 
{J. W. Spencer: ‘“‘ The duration of Niagara falls,” as above, pp. 464-468. 
7J. Pohlman: ‘“‘The Niagara gorge.” Proce. Am. Assoc. Ady. Sci., 1886, pp. 221, 222; also in Trans. 
Am. Inst. Mining Engineers, 1888. 
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