ONTARIO COUNTY. 
457 
it. In Ontario county it follows the same course, and can be seen a little south of its out¬ 
cropping edge. It is recognized by its darker blue color, fine texture and homogeneous struc¬ 
ture; it is generally very brittle, breaking with a slight blow of the hammer, while in some 
localities it furnishes stone fit for building. 
The Marcellus shale, and the shales of the Hamilton group, appear at numerous points in 
this county ; and after leaving Geneva, they may be seen in nearly all the ravines and banks 
of streams which flow towards the north. The banks of Canandaigua lake also afford good 
opportunity of examining these rocks. In other parts of the county, the accumulation of 
drift is so great as to offer few exposures of these shales. 
The Tully limestone appears on the shore of Seneca lake, at Bellona, in the bed of Flint 
creek at Bethel, and about four miles northwest of this point. Before reaching Canandaigua 
lake, however, this rock has entirely thinned out, though its place in the shales is well defined 
for many miles along the shore. 
South of the range indicated by this limestone, there is a width of from one to three miles 
of the Genesee slate, but this rock is only seen along the ravines. The gas springs of Bristol 
and other places rise from this shale, or the lower part of the group next succeeding it. 
The Portage group occupies the towns of Naples, Canadice, and the south part of Bristol, 
and presents the same essential characters as described in Seneca county. The sandstone 
portions are used for flagging stones, and, when sufficiently thick, for building stones. 
These rocks are seen to great advantage in the deep ravines about the head of Canandaigua 
lake, and in the banks of the Honeove, Canadice and Hemlock lakes. These three lakes at 
present join their outlets, producing the Honeoye creek, which has been excavated since the 
deposition of the drift; and the rocks are exposed along its whole course. The original 
outlet of these valleys was probably farther east, and joining the present Irondequoit, passed 
into Lake Ontario by that channel. These valleys also extend south, and meet the Conhoc- 
ton, showing that at some former period the course of the water was not restricted within its 
present limits, but extended south to the Tioga or Chemung. Thus a stream whose width 
embraces the valleys and beds of the lakes in this direction, may have passed southward from 
Lake Ontario to the Susquehannah ; or, otherwise, a stream from the south may have flowed 
along the Conhocton and these valleys to Lake Ontario. It is quite evident, from the extent 
of the valleys and the alluvium piled up in their course, that few of our streams in an earlier 
geological era had their present origin, or were limited to their present extent. Every valley 
and every rock bears marks of the great body of water of which small under currents merely 
wore the course of the present valleys, while the mighty whole passed over the summits of 
our highest hills. 
The principal mineral resource of this county is gypsum, the situation of which has already 
been described. There are several marl beds of importance; the most extensive one is in a 
marsh bordering Flint creek, south of the village of Bethel. Large quantities could readily 
be obtained at this place, and it would prove a valuable acquisition to the farmer, especially 
[Geol. 4th Dist.] 58 
