No. 275.J 311 
which fill the yalley covered, in the former case, with alluvium. The 
beds of both lakes seem to be where the strata were onginally more de- 
pressed than either on the east or west, consequently at a period when 
the whole surface was covered with water, this would be the natural 
course of the current. From some cause it appears to have divided and 
taken the two channels of Cayuga and Seneca lakes, and to have found 
its outlet far south, after joining other currents from different quarters. 
From Jones' quarry we trace the limestone westward. It appears on 
Flint creek, above Vienna, and at several points along streams between 
this place and the Canandaigua outlet. In the bed of Flint creek, and 
also on the outlet, it contains a large quantity of hornstone, which, on 
weathering, gives the mass a peculiarly rough and ragged appearance. 
It is exposed in the bed and banks of Mud creek, at Lapham's mill; 
and here we procuied a fine specimen of Icthyodorulite. This fossil has 
been found in the same limestone at Waterloo; and an exceedingly 
beautiful specimen is preserved in the cabinet of David Thomas of Au- 
rora. At the last named locality in Ontario county, the upper part of 
the Seneca limestone is light gray or almost drab, very fine grained and 
compact; it contains a trilobite, Asaphus, with the post-abdomen armed 
with two spines, and well merits the appellation of spinulurus. This 
rock is quarried in many places, both for building stones and lime. 
For the latter purpose the upper layers are preferred; they break readily 
into thin pieces, and contain great numbers of Orthis affinis, or a similar 
one, and Strophomena rugosa. Quarries are worked near Oak corners, 
along the Canandaigua outlet at Bates' mill, Gardners, &c. west of the 
outlet between this and Mud creek, and other places. 
The Seneca limestone embraces a shaly stratum, containing great 
numbers of a small fossil, resembling a Cytherina, so minute as scarcely 
to be distinguishable by the naked eye; and in some instance* the stone 
is literally made up of these shells, appearing to have been once a liv- 
ing mass. This stratum is well exhibited in IVTud creek, on the Canan- 
daigua outlet at Short's mill, and near the Eagle mill on Flint creek; 
through which extent it bears a very constant character. 
The Onondaga and Seneca limestones occupy, throughout this' county, 
a width of two miles; varying somewhat along the streams w^hich have 
exposed the southern rocks and worn down their northern edges, leav- 
ing a slight curve to the south. The whole northern edge of these 
rocks presents an undulatory or indented outline; some points extending 
a mile further north than the alternating indentation. 
