178 
GEOLOGY OF THE FOURTH DISTRICT. 
dication of coal; and throughout the district, and even the whole length of the State, it has 
been bored or excavated in search for this mineral. This example affords an exemplification 
of the reasoning and practice in the absence of geological knowledge, and shows most clearly 
the benefits which may be derived from understanding the order among our rocks, and the 
true place of the coal-bearing strata. 
This rock first appears in the district in Seneca county, where it succeeds the Corniferous 
limestone. There are one or two natural exposures of the same south of Waterloo village, 
and it approaches within a few feet of the surface entirely across the county. The portion 
most exposed is black and very fissile, separating into thin laminae, from the presence of great 
numbers of a smooth Avicula, which is everywhere an abundant fossil of this rock. It is 
exceedingly thin and fragile, and usually appears in fragments upon the surface of the laminae. 
Its form is obscure, though when perfect there is no doubt of its character. 
In the excavation of wells a short distance south of the point where the limestone disappears, 
this shale is usually thrown out; and it can always be distinguished by the shell just men¬ 
tioned, and flattened fragments of an Orthoceras, as well as by its peculiar black color. 
The same rock appears about two miles south of Vienna, in the banks of Flint creek. The 
portion exposed is very fissile from weathering, and its color externally is somewhat greyish. 
The same thin stratum of limestone which holds a place in the shale in other places, appears 
at this locality. It contains a large number of Orthocene and a species of Euomphalus, but 
the interior is usually lined with crystalline matter, and the shell is very fragile. At this place 
I found a fragment of the Dipleura Dekayi, which is the lowest position in which I have seen 
this fossil. The shale also appears about two miles southeast of Vienna, and near the point 
where the limestone disappears beneath the surface. 
The bed and banks of Flint creek in Bloomfield exhibit this rock in a good degree of per¬ 
fection, and well marked by its peculiar fossils. The outlet of Conesus lake, a little west of 
the village of Avon, is one of the best exposures of the rock in the district. The lower part 
is black and fissile; about twenty feet higher, the mass is more compact, very black, and 
highly bituminous. It contains large accretions of siliceous limestone, which are sometimes 
quite pure, at others intermixed with shale. The stratum of limestone is compact, about a 
foot in thickness, and filled with fragments of fossils. The rock just below and above this 
limestone is very fissile, readily separating into broad slaty laminae, the surfaces covered with 
organic remains. 
On the west side of the Genesee river, it appears about two miles south of Caledonia village, 
where it has been bored in several places in search of coal. At this place, and a short dis¬ 
tance farther north, it presents its usual characters both of compact and fissile structure. 
At Le Roy village, this rock is well exposed to view in ihe bed of Allen’s creek. The 
lower part of the shale is mostly compact, with little tendency to lamination, while the higher 
portions are very fissile. It contains a great abundance of concretions or Septaria, which are 
plentifully distributed through the mass at about the level of the creek, and below the fossili- 
ferous portion of the rock. These concretions are of a siliceous limestone, apparently resulting 
from a small quantity of the material spread over the surface, which being too little to con- 
