70 F. B. TAYLOR—ORIGIN OF GORGE OF WHIRLPOOL RAPIDS. 
old hydraulic canal (about a quarter of a mile below the carriage bridge), 
where the soundings show a depth of over 160 feet. In the lower two- 
thirds of the Upper Great gorge the extremes of top width are about 
1,000 and 1,300 feet, so that the top width of 1,200 feet for the Eddy 
basin is not far from the mean of that section. From such a comparison 
it seems probable that the Eddy basin was made by the great cataract 
with the same volume as it had in the Cove section, and the same as it 
has now. While this correspondence of magnitudes does not prove iden- 
tity of origin absolutely, it is nevertheless true that there is apparently 
no fact or circumstance which can be offered in disproof of it. The 
Whirlpool basin itself indicates nothing as to the volume of the modern 
river at the time the drift was cleared out. Unless we suppose a sudden 
change of volume to have occurred just then, we should look for the re- 
appearance of gorge characters like those of the Cove section at some- 
- point above the Whirlpool—wherever the new cataract resumed work. 
The Eddy basin has these characters, and it seems natural, therefore, to 
associate it with the Cove section, putting the two together as one con- 
tinuous piece of work, interrupted and separated only by the compara- 
tively brief incident of the Whirlpool washout. These two sections taken 
as a unit may be called, provisionally, the Middle Great gorge. 
One other circumstance seems to lend strong support to this interpre- 
tation of the Eddy basin. This basin is a deep hole to the south of or 
behind the shoal ledge which lies between it and the Whirlpool, and — 
was made after the ledge had been passed. With such width, and with 
the great or very considerable depth that it appears to have, it seems 
well nigh certain that it was made by a large cataract. In that case it 
must belong either with the Saint Davids preglacial gorge, supposing 
this to have been made by a great cataract, or else with the Cove section 
of the modern gorge. It can hardly be attributed to a small stream in 
any event, because a small stream would not have bored out so large and 
deep a hole behind the ledge. A small cataract falling into a deep pool 
of water has little or no power to excavate at its bottom, and it seems 
plain, therefore, that a small stream would not have made a hole so wide 
and deep as the Eddy basin. Thus, whatever its age, it is in all proba- 
bility the work of a great and not of a small cataract. This greatly in- 
creases the probability that it is of modern origin, for if it is preglacial 
and a part of the Saint Davids gorge, why should the shoal ledge be 
there? Some special explanation will have to be invented for the ledge 
and the associated contraction of width if this view is to be maintained. 
Eddy basin and the gorge of the Whirlpool rapids.—If it be granted 
that the Eddy basin was made by the modern great cataract, then there 
follows very closely another important conclusion, namely, that the 
a 
