76 F. B. TAYLOR—ORIGIN OF GORGE OF WHIRLPOOL RAPIDS. 
Some idea of the size of this river may be gathered from observations 
made at Des Epines rapids. At that place the maximum depth was 
about 55 feet, with a mean of between 30 and 40 feet. The width was 
estimated to be between 600 and 700 feet, and yet the current at this 
place was strong enough to make potholes in many boulders. These 
dimensions resemble very closely those of the present Saint Clair river 
in “the rapids” at its head, a mile or more above Port Huron, where 
the current is nearly five miles an hour. The action of this current as 
it rolls along good-sized grains of sand may be seen at the upper end of 
the dock at Point Edward on the Canadian side. 
Talon gorge.—At Talon chute, a little below the foot of Talon lake, was 
situated the only fall or cascade of the Nipissing-Mattawa river. Here 
the river fell over a ledge of “ massive flesh red gneissoid granite,” * at 
first about 40 feet high, but later apparently 10 or 12 feet lower. Below 
the chute is a canyon nearly half a mile long, approximately 200 to 400 
feet wide, and with vertical walls 20 to 60 or 70 feet high. Except near 
the upper end, it has the appearance of being very deep. At the lower 
end the rocks are heavily glaciated, showing the usual rounded smooth 
forms, but in the upper part the walls give no evidence of glacial modi- 
fication. The gorge widens somewhat toward its lower or eastward end. 
Judging by faint old shorelines on the slopes of Talon lake 2 miles above, 
the water passing over the brink of the falls was 15 to 20 feet deep. On 
the granite ledges, near the crest of the falls, there are a considerable 
number of potholes, mostly not deep. Some of them are 10 feet or more 
above the present water, and their size and wide transverse distribution 
indicates a large volume for the stream that made them. The boring of 
these potholes out of the hard granite implies in this instance a long 
duration of time, for the river here issued almost directly from Talon 
lake, the largest in the lake chain of that time, and must therefore have 
carried very little coarse-grained sediment. A few smaller, deeper pot- 
holes were found in the limestone also. When the great outlet river 
abandoned its channel the falls had become divided in two parts around 
a high rockyisland. In the south branch of the canyon there is a thin, 
highly inclined bed of crystalline limestone, and this arm of the gorge 
is the narrower and the longer of the two. So far as could be seen, the 
limestone did not appear to extend more than a few rods below the falls, 
but its strike was apparently about in line with the gorge, and it is pos- 
sible that it may have had an important influence in determining the 
direction of the gorge and the rate of its making. At the chute the 
south branch of the canyon follows this bed of limestone, while the 
north branch is cut out of the red granite. The modern river with its 
* Ells and Barlow: As above, p. 169. 
