Part I. Report of progress in 1869, by J. S. Newberry, chief geologist. Part II. Report of progress in the second district, by E. B. Andrews, assist. geologist. Part III. Report on geology of Montgomery County, by Edward Orton, assist. geologist.

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The Niagara limestone has considerable economic value, inasmuch as
it furnishes much of the lime used in building in various portions of the
State, and is the rock so highly esteemed in southwestern Ohio, known
as the Dayton-stone.
THE SALINA AND LOWER HELDERBERG FORMATIONS.
The Niagara is succeeded in the' ascending scale by the Salina and
Water-lime groups which form the summit of the Silurian system. These
strata are so named, because the first and lowest contains the salt and
gypsum of central New York; while, the upper, as its name implies, is
characterized by the presence of hydraulic lime, and is the formation
which furnished the hydraulic cement manufactured in Western New
York and Louisville, Kentucky.. These two limestone beds, with two
others and a bed of sandstone which overlie them, and the Clinton and
Niagara below, were united under the name of the Cliff limestone, in the
reports of the former Geological Board. One of the results of our past
summer's work has been to resolve this Cliff limestone into its component parts, and to show that it includes seven distinct formations, belonging to two great geological systems. Up to the time of the organization of the present survey, it may be said that only one of the formations
composing the "Cliff" had been distinctly recognized-the Corniferous
limestone, that of which the State House is constructed. Evidence of
the presence of the Niagara had been obtained, but nothing definite was
known with regard to its geographical position, thickness, or relations
to the associated rocks.
The manner in which the water-lime group was identified will serve to
illustrate the way in which the different members of our geological series
have been investigated and their. ages determined. It is now a wellrecognized truth, that paleontology is an indispensable aid to the study
of our sedimentary rocks. Each formation is characterized by a greater
or less number of fossils, which are found only in them.
In the identification of the water-lime group, I was guided entirely by
its fossils. The most easterly of the islands in Lake Erie, Kelley's
Island, was, I knew, composed of the corniferous limestone, as it is full
of fossils characteristic of that formation; but the more westerly islands,
Put-in-Bay, North and Middle Bass, &c., are wrought out of a hard gray
limestone, generally without fossils, and apparently quite different from
any portion of the "Cliff," as seen in the southern part of the State.
In this rock, after much search, I discovered a little bivalve crustacean,
having the form and' size of a bean. This was at once recognized as
Leperditia alta, a fossil of the water-lime portion of the Upper Silurian
of New York. With the Leperditia at the East are associated two or
three other fossils, found only in the water-lime, and, for confirmation of