364 
I May 
ill regarding this as tlie coiitiimation of tlie preglacial valley. 
After entering the gorge, the tirst portion of which is cut into the 
left bank of the valley, the river again turns to the right, and. 
^ 
/^znurr^ 
l(r 
Fig. 2. Map of the Genesee Kiver at Portage. From a compass 
survey. Scale 1 in. = 5000 ft. Shaded portions indicate rocls: exposure. 
L. G. Lateral drift-filled gorge. 
ess than a quarter of a mile from the point at which it entered, 
it falls sixty-six feet, having described a horseshoe-shaped curve. 
Beyond this point the left bank recedes again from the river, 
leaving a plane tract of nearly a square mile at the river level. 
This tract, known as ''Glen Iris," has the form of an amphitheatre, 
with hills on three sides and the river in the foreground. The 
right bank of the river, instead of being rock, is here formed of 
boulder clay with a covering of sand, this being, in fact, the 
other side of the ''Portage Ridge" before noted. Here, too, can 
be seen the exact outline of the drift-filled portion of the valley, 
the rock, near the Upper Falls, sloping to the level of the river 
beloio the falls, and rising again, less than a mile down stream, that 
is, a little bevond the Middle Falls. ^ An examination of the hills 
1 Professor Hall in the report of the ith district, p. 372, gives a description of this 
vallej', with a diagram. He also speaks of it on p. 345. 
