440 
[Assembly 
ther deposit spread over it, of materials from the south, consisting of 
flat masses of sandstone and scarcely worn pebbles, with loam, &c. 
distinct from that below. This deposit proceeded from a second erup- 
tion, after the first opening was closed up, and was probably made at 
the period when the river commenced flowing in its present course. 
There are several other places between Portage and Mt. Morris, 
where the direction of the river has been changed since it commenced 
its course through these rocks. The chasm for two or three miles 
' above Mt. Morris bridge, appears more recent than some portions be- 
tween that place and the lower falls, and it is not improbable that a 
portion at least of the waters of this river flowed through a gorge little 
to the north of the present one. The valley by way of Silver Lake, 
has at one tnne served as a water course, probably for the waters of 
the lake above Portage. 
A partial history is thus presented of the changes which have taken 
place in the Genesee valley ; further and more minute investigation 
will doubtless detect others, though of less importance and magnitude 
than those enumerated. Although the same phenomena are exhibited 
in other valleys, I have seen none where they are exhibited so clearly. 
The Genesee valley is a prominent feature in the surface of the 
counties of Livingston and Allegany, all the others are of minor im- 
portance, or lateral and tributary valleys. That of Conesus Lake is 
an inconsiderable one, the depth of the lake being but fifty-seven feet ; 
the valley in its continuation south joins the Genesee valley north of 
Dansville. 
The valley of the Caneadea creek has probably drained a lake which 
once existed in the neighborhood of Rushford village. Many of the 
deep ravines, some of them with small streams still flowing into them, 
are the outlets to higher lakes which have been thus drained. 
The principal valleys west of the Genesee, are for the most part not 
so well defined or continuous, though some of them are deep. In Ge- 
nesee county, we have the valleys of Allen's and Tonawanda creeks ; 
towards the sources of these streams the valleys divide, and gradually 
rise to near the general level of the surrounding country, still their 
course can be traced joining the valleys extending south to the Allega- 
ny. The more elevated country, between these north and south val- 
