Grabru..] 366 [May i6, 
we find, aftei" rising several hundred feet, that this valley communicates 
with the valley of the Canisteo River, and thence with the Chemung and 
Susquehanna. The Genesee Kiver, beyond Portage, flows in a valley 
more than Ave hundred feet above the same, after leaving the gorge at 
Mt. Morris. The northern part of this valley, from Rochester to Dans- 
vlUe, maiutams nearly the same elevation throughout, or with a gradual 
descent to the north. It is one of the most ancient valleys of excavation ; 
and its sloping sides, covered with superficial accumulations to the height 
of 600 or 800 feet above its base, show an immense period of time to 
have elapsed since its formation. Long subsequent to its formation it 
has been partially filled Avith water, having a barrier on the north, and 
extending over the whole plain of the ''Genesee flats," and south as far as 
Dansville, in one great shallow lake. At the same time the valleys south 
of Dausville and south of Mount Morris, by way of Cashaqua Creek, 
were discharging their waters into this lake. With these streams was 
brought down a large quantity of coarse aud fine materials, which we 
now find about Dansville, and below the junction of the Cashaqua Creek, 
while the great extent of the valley is spread over with a fine sandy 
loam." 
It seems quite probable that, as Professor Hall suggests, the 
valley was prolonged southward beyond Dansville, and that the 
divide between the head waters of the Canisteo and those of the 
Caneseraga is of later origin. Not having examined this region 
personally, I am unable to make definite statements regarding it. 
If the valley by way of Arkport and Hornellsville is the south- 
ward i^rolongation of the Dansville-llochester Valley, Ave have 
our preglaeial river of a length approaching that of the modern 
Genesee, This supposition seems to be favored by the character 
of several of the smaller streams, esjjecially of Bennett's Creek 
which flows neaijy directly north and joins tiie southeast flowing 
Canisteo by a short, sharp bend. 
Perhaps the most approi)riate name for this river Avill be the 
preglaeial Caneseraga, since the valley from Dansville to Mt. 
Morris is to-day occupied by this stream. The distance between 
the ]>reglacial Genesee and the preglaeial Caneseraga was about 
eighteen miles at Dansville, and about fifteen miles at Mt. Morris. 
Seneca and Cayuga Lakes are eighteen miles apart at their 
southern ends, their shores approaching to within seven or eight 
miles near the center. 
Condition of the valleys on the recession of the ice. — When the 
ice front had receded to near the southern margin of Lake Onta- 
rio, it formed a barrier across the northern end of the valley of 
