506 
GEOLOGY OF THE FOURTH DISTRICT. 
giving evidence of a period of disturbance. These suggestions are offered, not with any view 
to merge in one formation what can be regarded as decidedly distinct, but with the desire to 
offer some facts toward the foundation of general groups or classes, to which all the numerous 
minor subdivisions may be referred. 
The junction of this group with the cliff limestone cannot be seen in the neighborhood of 
Cincinnati; but in passing down the river, the two appear in juxtaposition before reaching 
Madison, Indiana. In the Ohio reports, Dr. Locke refers to this place as exhibiting, in a very 
perfect manner, the contact of the two rocks, cliff and blue limestones, which are well seen 
in the deep cutting for the railroad one mile southwest of the village, and in a ravine still 
further below. 
The fossils of the blue limestone at this place illustrate the same view as at Maysville and 
Cincinnati. The Pterinea carinata, with one or two species of Cypricardia , are common; 
while Strophomena, Orthis, and others, abound in the middle portions, together with the 
Atrypa capax of Conrad, a species not seen at Cincinnati. Large numbers of Cyathophylli 
occur of a species different from any of the higher rocks. Near the junction of the blue and 
cliff, which latter is strongly contrasted in color, as well as other characters, there occurs a 
stratum of twenty-five feet thickness, of a greenish grey sandy shale, containing Cypricardia 
modiolaris, and numerous spherical masses of coral, (Porites ?) which lie in two courses, or 
ranges, near the top of the mass, and separated by a few feet of shale from each other. Some 
of these masses attain a large size, being three or four feet in diameter, while others arc but 
a few inches. 
The lower member of the cliff limestone, at this place, is a calcareo-siliceous mass, with 
green stripes and spots, and crumbling on exposure to the air. It appears quite destitute of 
fossils, so far as I could discover. About fifty or sixty feet above the base of this mass, I 
noticed a strong ferruginous exudation ; but the point being at the junction of the rock with 
the loose materials above, I was unable to discover any ore in place. This rock, which 
plainly succeeds the shales and limestones equivalent to the Hudson river group, is marked 
by patches and laminae of green shaly matter, strongly resembling some portions of the inter¬ 
mediate mass between the Medina sandstone and the Clinton group, being an intermixture of 
the green shale of the one, and the sandy matter of the other. 
Time, however, did not admit of going into detailed examinations, regarding the individual 
rocks, or groups, composing the cliff limestone, the object being a general identification of 
larger subdivisions. From examinations made at a short distance from this place, I learned 
that the friable sandy mass just noticed was succeeded by a harsh, porous limestone, appa¬ 
rently magnesian in composition, and possessing the general characters of the Niagara lime¬ 
stone in New-York. At this place I was unable to find any fossils save a few crinoidal 
columns, which gave to the rock much the appearance of the lower part of that at Niagara 
falls and Lockport. The examinations of this rock in other places, where I found fossils, 
and was able to trace the succession upwards, left no doubt of its identity with the Niagara 
rock. 
It should be remarked, that soon after leaving Cincinnati, the rocks are seen to dip to the 
