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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However unsuccessful as regards the purpose for which it was bored,
this well gave us interesting evidence of the nature of the strata underlying those which are exposed to sight in our State. These were plainly
the Calciferous sand rock (here containing much more lime and magnesia
and less silica than in New York) and the Potsdam sandstone, which
had not been passed through when the work was arrested.
THE CINCINNATI GROUP.
The Cincinnati or blue limestone group is exposed in the southwestern
corner of the State (that surrounding the city of Cincinnati), and extends southward into what is called the Blue-grass region of Kentucky.
The reason why over this area the Lower Silurian rocks are exposed,
while all the country about them is occupied by more recent formations,
is that it lies on the line of a great arch or fold of the strata, which runs
parallel with the folds of the Alleghany mountains, and was doubtless
produced by the same cause. Subsequently to the elevation of this
arch, the rocks forming its summit were extensively removed by surface
erosion, and thus the lower strata were exposed to view.
The thickness of the Cincinnati group is about,1,000 feet. It is interesting both from the number and variety of the fossils which it contains
(mollusks, corals, crinoids and crustacea), and also for the fertility of the
soil it has furnished. By reference to the map it will be seen that the
margin of the blue limestone area is extremely ragged and irregular.
This is an accurate representation of nature, however, for Prof. Orton
has traced this line with the greatest care. Its sinuosities are due to the
excavation-and removal of the overlying rocks by all the tributaries of
the Little Miami; thus the valley of each stream forms a narrow or wide
prolongation of the blue limestone surface, while the divides are composed of more recent rocks.
THE CLINTON AND NIAGARA GROUPS.
These are parts of the Upper Silurian system, and are mostly limestones, the Clinton from 10 to 100 feet thick, according to the locality
where it is observed, the Niagara about 80. The lines of outcrop of
these rocks are nearly parallel with each other and to the margin of the
blue limestone, and along this line the Clinton makes its only appearance
in the State; but the over-lying Niagara, concealed in the central portion of the State by over-lying strata, presently to be mentioned, reappears on the lake shore and forms the crown of the arch to which I
have referred, down nearly as far as Bellefontaine. The Clinton group
will be remembered by many when I say that it forms the cliffs bordering the Genesee below the falls, at Rochester; the Niagara, that it composes the shelf over which the water pours in the great cascade from
which it is named.