220 The American Geologist. March, 1894 
tiary times, and spreads out over it. This is unquestionably in the area 
of the earliest drift, hence the rock gorge must be entirely preglacial. 
On the south side of the Allegheny at Clarendon, four miles from War- 
ren, there are extensive gravel deposits, with granitic pebbles, rising to 
about the same hight with the terrace described on the Conewango, 
and rilling a buried channel 250 feet deep. This is on the watershed 
between the Allegheny and the Tionesta. This rock gorge must be 
wholly preglacial, yet it extends down very closely to the level of that 
of the present Allegheny. Such an amount of preglacial erosion there 
would be inconsistent with a less amount anywhere down the Alle- 
gheny and Ohio. 
According to Prof. Wright, the amount of glacial gravel preserved on 
the 200 to 250 feet rock shelves of the Allegheny and upper Ohio has 
not been at all appreciated until within the past year. These gravel 
accumulations line the gorge throughout nearly its whole length and 
are often a half mile wide and 50 feet deep. Assuming it to be proved 
that the erosion of the rock gorge was preglacial, the whole valley must 
have been afterward filled with gravel derived from the ice-sheet and 
then re-excavated. Both these processes were probably aided by the 
Cincinnati ice dam formed by the advance of the ice-sheet there across 
the Ohio valley, which, by producing slack water as far up as Oil City, 
retained all the early glacial sediment and so hastened the filling. 
Later the removal of the ice dam gave an increased gradient to the 
stream, so that its re-excavation was greatly hastened. While, there- 
fore, not questioning Prof. Chamberlin's estimate of the amount of ma- 
terial eroded since the tilling up of the gorge, the time supposed is less 
because the material was all loose and the gradient much larger than 
now, while also the glacial floods still supplied a larger flow of water. 
53. Tin- ancient strait at Nipissing. F. B. Taylor, Fort Wayne, 
Ind. (Read by title.) The following facts relating to the shore lines of 
the postglacial submergence in the vicinity of lake Nipissing, Ontario, 
were gathered bv explorations during the past season. On the hills 
north of North Bay four distinct beaches were found. Measured by 
aneroid from North Bay station, which by the C. P. R. profile and Dr. 
J. W. Spencer's table of altitudes in Canada is G58 feet above mean tide 
in the Culf of St. Lawrence, their altitudes are about as follows: 1. 
Nipissing beach, 743 feet. 2. Thibeault beach, 1,005 feet. 3. McEwen 
beach, 1,090 feet. 4. Nelson beach, 1,140 feet. The Nipissing beach 
marks the level of the Great Lakes during the time of the active river 
outlet eastward down the Mattawa to the Ottawa. This beach is de- 
veloped in great strength and was seen at many points westward as far 
as Duluth, Minn. It rises slightly from west to east. The other three 
beaches are distinct ridges of rounded gravel facing lake Nipissing. The 
Nelson beach marks the upper limit of submergence. No evidence of 
submergence was found on higher ground there, but on the hills south- 
east of North Bay the shore line was found at about 1,205 feet near 
Sundridge and about 1,220 feet near South river. 
About 125 miles west of North Bay heavy gravel deltas of the Ohnap- 
ing river and streams flowing into Windy lake were found near the top 
of the grade eight miles east of Cartier on the C. P. R. at an altitude of 
about 1,200 feet. 
These facts point to the following conclusions: 1. That the upper 
three of the great lakes tributary to the St. Lawrence had a river out- 
let eastward across the Nipissing pass for a considerable time; 2. That 
there was before that time a strait over the Nipissing pass about 25 
miles wide and more than 500 feet deep; 3. The observations near Car- 
tier prove a wide extent of water in that direction. Hypothetical ex- 
tension of the plane of the Nelson beach and Ohnapingdeltanorthward 
over low lands suggests another strait over lakes Tamagaming and 
Temiscamang, and over the hight of land and lake Abittibi to the basin 
