Davis.] 
360 
[January 18 , 
of the old glacier, peculiar in form and remarkable in erosive 
power; the supposition that it is the result of down faulting or 
local subsidence, is negatived by the absence of disturbance in 
the neighboring hills ; to call it a rock-basin is entirely unwar- 
ranted, for its prolongation north of the lake is across a great 
drift-area, without rock in place. 1 The form of the trough 
is different in no important particular from valleys of evident 
erosion in non-glaciated regions. 
The gentle escarpment of the plateau in which the lakes are 
sunk runs a little south of a line from Syracuse through Auburn 
to Canandaigua; not far north of it is a broad irregular belt 
of drift-hills, of peculiar form, that must be considered an old 
moraine remodeled by an advance of the ice over it 2 ; north 
of Cayuga Lake these hills disappear and are replaced by a broad 
marsh, closely at the level of the lake ; but I believe this disap- 
pearance is only apparent; the hills are pretty surely there, but 
are buried beneath the marsh, because being deposited in the old 
valley trough, their summits reached a less elevation. The marsh 
itself is peculiar ; an alluvial flat usually occurs at the head of a 
lake by its inlet, not at the foot, by its outlet, as here 3 ; its 
inverted position is to be explained by considering it of the same 
origin as the flat prairies of northern Ohio (C. 2) ; it is made 
of detritus washed from the melting glacier, when during its final 
retreat it stood near the southern shore of Lake Ontario, and 
held up a large body of water south of its margin. Cayuga Lake 
(with its companions, so far as they agree with the above sugges- 
tion) is therefore like so many others, of double origin ; being 
due partly to a morainal barrier, and partly to a stratified drift 
deposit, which would carry it into the next species. 
1 This is more distinct for Cayuga Lake than for the others, but I believe it is essen- 
tially true for all. 
2 This conclusion rests upon my own observations, confirmed by suggestions from 
Messrs. G. F. Wright and R. Pumpellv. Since writing the above, I find an article 
on the Parallel Drift-Hills of Western New York, by Dr. L. Johnson, in the N. Y. 
Acad. Sci., Trans., i, 1882, 77-80. The hills are considered of subglacial origin, but 
the lakes near by are referred to as examples of glacial erosion. 
3 The outlet of Seneca Lake which enters Cayuga at its foot cannot have deposited 
the marsh alluvium, for its postglacial erosion has been insignificant, as is shown by 
the form of the country through which it runs. 
