HAMILTON GROUP. 
189 
In these towns there are numerous good exposures of the group, the best of which are 
along Canandaigua lake and in the ravines upon either side. The banks of Flint creek also 
afford a good opportunity of examining the whole series, and the several subdivisions as enu¬ 
merated may be found between Vienna and the village of Bethel, where the Tully limestone 
and Genesee slate succeed this group. On the north of the turnpike from Geneva to Canan¬ 
daigua, there are several ravines which disclose these shales in great perfection. The parts 
of the group here exhibited are principally the encrinal limestone and the shales below, which 
abound in fossils. The upper part of the division, denominated Ludlowville shales, is well 
marked by great numbers of Delthyris mucronatus and Atrypa concentrica , with one or two 
species of Strophomena; the lower part contains large numbers of Cypricardia and Avicula, 
and is more sandy in character than that above. The same portion of the mass is also well 
developed on Canandaigua lake, where its fossils are numerous. The lower part of the group 
is also seen, as well as the Moscow shale above. 
In Livingston county this formation occupies nearly the whole of the towns of Avon and 
York, a part of Geneseo, Leicester and Caledonia. The deep valley of the Genesee, with 
numerous lateral ravines and water courses, renders this county one of the most desirable loca¬ 
lities for examining the rocks of this group. The Moscow shale receives its name from the 
beautiful development of the same on Beard’s creek, on the land of Mr. Horsford ; and it con¬ 
tains at this locality more than fifty species of fossils, many of which do not occur in any part 
of the group below. The rock at this place is a pure calcareous mudstone, of a bluish color 
on first exposure, but weathering to a whitish ashen. Its decomposition is hastened by the 
diffusion of iron pyrites, which sometimes replaces the fossil bodies. At this locality the 
Genesee slate succeeds, without the intervention of any other rock. Several miles north 
of this point, on the land of the Hon. G. W. Patterson, the shale is well developed in a small 
ravine, and also at one or two other places in the immediate neighborhood. 
About three fourths of a mile west of York centre, there is a fine development of the shale 
immediately below the encrinal limestone. The latter also appears here in the form of a shaly 
limestone, with numerous crinoidal stems and other fossils. The shale is completely charged 
with Cyathophylli of different species, Favosites and other corals, with some trilobites and 
shells. In following down this ravine towards the river, the lower divisions of the shale are 
but obscurely seen, till we arrive at the thin division, before mentioned as the calcareous blue 
shale (or shaly limestone), which at this place is compact, and a tolerably pure limestone. 
On the east side of the river, at Jacock’s run, the Moscow shale, Encrinal limestone, and 
the higher part of the Ludlowville shales, are well exposed, and offer an abundance of fine 
fossils, among which are several beautiful corals of the genus Retepora or Fenestella. By 
following this ravine towards the river, the lower division of the group may be seen. At an¬ 
other ravine a mile or two farther south, the same shales are exhibited in a good degree of 
perfection. 
The Moscow shale is seen near the base of the fall on Fall brook, south of Geneseo village. 
The same is also seen near the Conesus outlet, and along that stream the lower divisions of 
the group are well exposed at several places. 
