4 
CHARACTERS OF THE UPPER GREAT GORGE. 638 
below the American fall and just opposite the inclined railway it is about 
1,350 feet, and in midstieam, where the deepest sounding in the river is 
found, it is 189 feet deep. Thence, for about a mile and a half or nearly 
down to the railroad bridges, the width varies between about 1,350 and a 
little more than 1,000 feet, the narrowest point being midway between the 
attiage and railroad bridges. At a point 35 or 40 rods above the upper 
railroad bridge the gorge suddenly grows narrow and shallow, and this 
is the beginning or head of the gorge of the Whirlpool rapids. The dis- . 
tance from the Horseshoe fall down to this place is about 2 miles. 
Throughout this section the dimensions of the gorge are remarkably 
Uniform, except in that part which lies opposite Goat island and the 
American fall, but the increased width here is not more than may be 
readily accounted for by the widening of the river bed above the falls 
when the cataract was passing this part of the gorge. It seems quite 
éettain that whenever the falls grew wider than usual and the water im 
consequence potired over the brink ina thinner sheet, then the power of 
the falls to excavate in the hole below was reduced. We should expect, 
therefore, to find the expanded parts of the gorge generally shallower 
than the parts of average width. So far as the scanty soundings go, they 
seem to support this expectation. It appears to be quite certain, there- 
fore, that the slight expansion of the gorge near the falls is not an indi- 
cation of increased volume, but only of increased width of the river bedl 
above the falls. There is apparently nothing in the section above the: 
gorge of the Whirlpool rapids which suggests variation of volume. This; 
is, of course, the most recently made section, and it has evidently beem 
made solely by the action of the great cataract with substantially the: 
same volume as now. Inasmuch as there are other parts of the gorge: 
farther down that have substantially the same dimensions, it seems: 
appropriate to call this section the Upper Great gorge. On account of its 
newness and the greater degree of certainty concerning the conditions 
attending its excavation, this section will be taken as the standard of 
comparison for the rest of the gorge. 
GORGE OF THE WHIRLPOOL RAPIDS 
Next below the Upper Great gorge is the gorge of the Whirlpool rapids: 
three-fourths of amile long. Its top width throughout most of its length 
is close to 750 feet, with a minimum of a little over 700 feet and a maxi- 
mum of about 950 feet. This greatest width, however, is confined to one: 
po..nt near the head of the section. The section as a whole is very even 
from e,.4 to end. There are no soundings in this part of the gorge, but 
by the cary, application of a very simple method Mz G. K. Gilbert has 
