Correspondence. 135 
lake Ontario. Prof. Tarr ignores this tilting, yet ii has backed the Ca- 
yuga water to a depth of over 100 feel at the southern end of the lake. 
Therefore his data for comparing theancienl slope of the valley will not 
stand. With this warping removed, the lake would be reduced to a 
maximum depth of about 300 feet. I have been informed by well-borers 
that north of tlie lake they have penetrated to a depth of 200 and 300 
feel without reaching rock. This statement I do not think Prof. Tarr 
lias denied. Under these conditions there is no known rock basin at all, 
to have been excavated by glaciers. If his evidence of glacier erosion 
holds good, he must amend his thesis to glacial "•erosion of valleys" and 
not '■basins." 
Prof. Tarr also concludes that lake Ontario may be a rock basin, be- 
cause lie thinks Cayuga basin to be one. This I am willing to concede. 
although his present proofs do not make it sure that lake Cayuga occu- 
pies a rock basin. Bui again let me call attention to the fact that in 
places the St. Lawrence river channel is filled with drift to a depth of 
240 feet, so that the nearest rocky barrier closing the lake is only 500 
feet above the deepest sounding of t lie lake. Now the recent warping 
of the earth's crust in this region far more than accounts for such a 
barrier. Consequently, when the cause of a barrier is known, and can 
be demonstrated as often as necessary, there is no need to appeal to the 
glacial excavation of the basin, even if the old valley had been chan- 
nelled by ice. the course of which was oblique to the southern walls of 
the lake. .1. w. Spencer. 
July 5th, 1894. 
The Age of Niagara Palls. This note is written simply as a pro- 
test against anyone forming a conclusion as to m\ work on the historj 
of the great lakes, or forming judgments of the history of the lakes 
themselves, upon the strength of Mr. Upham's citations (Am. Geolo- 
gist, July. 1894) from m\ writings. It was I who first surveyed the Al- 
gonquin beach and found thai it proved that there was no connection at 
that time with the Erie basin, but thai there was a northeastern outlet. 
From the present outlet of the lake I surveyed this beach for about 500 
miles, and in my papers 1 nol onl,> stated thai the Algonquin beach 
crossed what is now the outlet of lake Huron below the present lake sur- 
face but also mapped it. Yet Mr. Upham now says: ••Careful study of 
Prof. . I. W. Spencer's maps .... of the Huron and Erie shore lines con- 
vinces me that the outflow of lake Algonquin at tin' time of the Nipis- 
sing beach wenl bj way of the present St. Clarrand Detroit rivers " 
The very opposite is shown in mj papers, and. if not. field observation 
not only of the Algonquin but several lower beaches would show the 
northern outlet adopted b\ Gilberl and myself, who were the first ol>- 
sen ers in i he region. 
This is nol the ftrsl time thai I have had reason for replying to Mi-. 
Upham when using my work, although ii is the lirsi time I offer a 
printed criticism. 1 1 i^ method of reasoning is << priori to maintain thai 
i he discharge of i he Niagara has always been equal to that of i he preseut, 
