310 I AsSEIUSLY 
Uie surfaces cannot be worked smootbj and where the stratum in place 
has been exposed, the mass is often fractured around the hornstone. — 
When the lower layers abound in chert, they contain few or no fossils, 
while those containing little of it are filled with them. Further west 
this rock is exposed at many points; at the Manchester sulphur springs, 
half a mile and two miles west of this, and again in the outlet a mile 
above Manchester village; from this point it preserves nearly a west 
course to Mud creek, near the residence of Judge Lapham. 
Last summer I examined a quarry of the same rock in Livingston 
county. This is opened for the purpose of supplying stone for the con- 
struction of locks on the Genesee Valley canal, and the engineer will 
do himself credit, as well as secure the permanency of the work, by 
using these in preference to any of the sandstones south; although the 
expense of transportation will exceed that of others which might be 
procured on the line of the canah 
The Seneca limestone succeeds the Onondaga, and in some instances 
alternates with it. In Ontario county it follows the same course, and 
can be seen a little south of the outcropping edge of the Onondaga 
limestone. It is recognized by its darker blue colour, fine texture and 
homogeneous structure; it is generally very brittle, breaking with a 
slight blow of the hammar, while in some localities it furnishes stone 
fit for building. Like the Onondaga, it contains much chert or horn- 
stone. At its eastern termination in this county, about half a mile 
south of Oak's cornersj on the land of Mr. Jones, it presents six dis- 
tinct strata, each separated from the next by a thin layer of shale or 
hornstone. 
The upper stratum bears evidence of the erosive action of water, as 
of a powerful current bearing hard substances along in its course. At 
this point the limestone suddenly terminates, as if broken off and re- 
moved, leaving an abrupt descent to the east; and reappears at a dis- 
tance of six or seven miles near Waterloo. The mass of limestone 
has evidently been removed from all the intermediate space, which once 
formed part of the valley of Seneca lake; and not only this rock, but 
all those in the same line north, as none are seen until we approach the 
shore of lake Ontario. In numerous places the bays extend inland to- 
wards Seneca lake, with which, probably, they originally communicat- 
ed, while the great depth of alluvium in many places along the shore of 
lake Ontario, conceals the rocks if they are present. The limestone is 
also removed from tlje space occupied by the waters of Cayuga lake, 
