CLINTON GROUP. 
05 
baryta, and crystals of carbonate of lime sometimes occur, the two latter in small nests or 
cavities. 
5. Upper Limestone of Clinton Group. 
The second green shale, like the first, is terminated above by an impure, thin-bedded cal¬ 
careous deposit; the layers, which are often exceedingly tough, are separated by narrow 
seams of green shale. This rock closely resembles the more calcareous portions of the lower 
limestone. In some localities it contains masses and nodules of iron pyrites, which, on de¬ 
composing, leave the spaces filled with anhydrous gypsum, and these sometimes occur in 
such profusion as to render the rock useless for building purposes. Again, it is more sparingly 
diffused, and only sufficient to discolor the surface on weathering. The lower part of this 
limestone is often deeply stained with iron from the decomposition of pyrites ; and from the 
general similarity of the two calcareous masses, one is often led to suspect the occurrence of 
a bed of iron ore in a similar situation. Toward the Niagara river it becomes more entirely 
calcareous, and contains less sulphuret of iron. 
Some of the strata are of crystalline structure, and greyish blue color, composed in a great 
degree of comminuted corals or other organic remains. From its unequal crystallization it 
becomes, like the Pentamerus mass below, a good fire-stone. This character, however, with 
the intermixture of siliceous and argillaceous earths, makes it generally unfit to be burned for 
lime. 
This division is eighteen feet four inches thick on the Genesee river, and continues through¬ 
out the district more uniformly than either of the others ; showing about twenty feet on the 
Niagara. In many places it extends beyond the base of the great Limestone terrace, and 
forms a narrow plateau to the west of Rochester, often quite exposed from the removal of the 
superincumbent earth. 
The more uncrystalline portions of this limestone dissolve on weathering, and leave the 
crystallized joints of crinoidea, corals and other fossils, standing out in bold relief. Thus is 
revealed in a clear manner the materials of the rock, as well as the changes that have been 
wrought upon them. These fragments of shells, crinoids and corals must once have formed 
parts of living and perfect individuals, which have lived at the bottom of the ocean, beyond 
the reach of the destructive agency of the waves; again they have been brought within such 
influence, and broken down, and their fragments ground together, till they formed the homo¬ 
geneous mass presented to the eye in the great body of this rock. Afterwards these materials 
must have constituted a beach, or bar of calcareous sand, extending beyond the limits of 
the district in either direction. This is the process of formation not only of this individual 
mass, but of nearly all calcareous deposits. The close alternation of deposits of purely argil¬ 
laceous matter, with those of calcareous composition, is another subject of the highest interest 
to the student in these subjects; they indicate changes in the depth of the ocean which have 
marked the different periods; and they direct us to the influence of causes which are now in 
operation upon the solid crust of the earth, and visible only by their effects in elevating or 
depressing the bed of the ocean. 
Geol. 4th List. 
9 
