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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formation in different localities has already been noted, the limits having
been given as from 5 to 50 feet. From the fact that so great variety in
composition is found in these rocks, we are warranted in concluding that
the Niagara strata were not originally of uniform thickness, as the beds
of the previous groups seem to have been. It may be that the higher
degrees of excellence in the stone were connected with a slower rate of
growth. It is at all events true, that the most valuable deposits of this
series in the county are, in every case, shallow.
The lower beds contain but very few fossils, some circular corals, and
very rarely a bivalve or chambered shell making out the list, while in
higher portions of the group, the strata are frequently crowded with fossils, which differ almost entirely in species from those that are found in
the lower groups. One peculiarity of these fossils is that they occur
almost always as internal casts, the outer shell or investment having
been.dissolved and carried away during the past conditions of the rock.
One of the most noticeable of all these forms of ancient life is the large,
bivalve shell-Pentamerus oblongus-known sometimes as the " deer-foot"
shell, and quite frequently identified as a petrified hickory-nut. The sections of a large chambered shell, of the genus Orthocevas, are also frequently met with, and are sometimes mistaken by the ignorant for the
back-bones of fishes or serpents.
The area occupied by the Niagara rocks is not probably more than onehalf of that which the Clinton covers. There seems, however, no reason
to doubt that both of these members of the Cliff formation were once extended over the whole surface of the county, as their present distribution
can be satisfactorily explained by reference to erosive agencies that are
known to have been at work upon them-agencies, some of which are
still continuing their destructive tasks. By referring to the map on page
158, it will be seen that the Clinton and Niagara, in the eastern portions
of the county, occur altogether in insulated masses or islands; on the
ridge between the two Miamis, and all the water-courses that flow from
these high grounds, have already worn their channels deep into these
rocks, not unfrequently completely through them, into the underlying
Blue Limestone series. There is, however, a manifest shallowing of the
Cliff rocks as we go southward, the Clinton diminishing to 9 feet near the
southern line of the county, apparently indicating that the Blue Limestone regions southward were, even at this early time, raised above the
surface of the seas, or, in other words, that they were never covered by
the limestones of the succeeding Cliff formation.
IV. DRIFT,
All of the formations above named are covered through almost their
entire extent with the deposits of the Drift Period-miles, in some in