120 The American (ieologist, Auffust, 18G6 
the latter case the surface of tlic lake must have fallen from 
its place at present lake level at Port Huron, Mich., in Saginaw 
bay, and at Two Rivers, Wis., to a level 500 feet lower or to 
within 80 feet of present sea level. Then there had to inter- 
vene time enough for about .500 feet of uplifts in the Mattawa- 
Ottawa region before the Nipissing beacli could have begun 
to be formed. We cannot say positively that this was or was 
not the course of events. It is a possible alternative. But it 
seems much more likely, and it apparently agrees better with 
the Niagara gorge, to suppose that the major part of the 
Algonquin uplifts occurred during the life of lake Algoncpiin 
and hence before the breaking away of the ice dam in the 
Ottawa valley. In this case when the break came the level of 
the lake at North Bay was not very much above the pass and 
the fall to the pass and to the level of the Nipissing beach was 
not great. But we do not know whether the change was 
directly to the Nipissing beach, the uplifts ceasing then alto- 
gether, or whether there may not have been some slight up- 
lifting at North Bay after the fall to the level of the pass. 
The whole subject of the Algonquin uplifts and their rela- 
tions to the lake history is extremely complex. While a large 
number of data have been gathered which bear on the questions 
involved, probably many more will be needed before any de- 
cisive conclusion can be reached. But injustice to the suliject 
and to those who have been most closely connected with its 
study it should be said that the data even now on hand have 
not yet been fully worked over. An account of submergence 
phenomena observed at lower levels in the Mattawa and 
Ottawa valleys will be given in another paper. 
THE ORIGIN OF THE WIND GAP. 
By Fred B. Wright, Oberlin, Oliio. 
(Plate III.) 
In the eastern part of Pennsylvania, on the boundary be- 
tween Monroe and Northampton counties, the outcrop of Me- 
dina sandstone which forms, as elsewhere, the even crest of 
Blue or Kittatinny mountain, is cut by the Wind gap. Below 
the hard capping of sandstone lie the softer strata of Hudson 
River shales and Utica slates. Descending the northern slope 
of the mountain you pass from the Medina sandstone to the 
