2 GEOLOGY OF OHIO. 
This is also proven by the Conglomerate of the Clinton, formed of peb- 
bles and rolled fossils of the Cincinnati Group, and the Conglomerate at 
the base of the Corniferous, composed largely of pebbles of the Water- 
lime. 
To the sketch of the structure and history of the Cincinnati arch, 
given in our first volume, we may add that there is apparently good evi- 
dence that during the Paleozoic ages the different portions of this arch 
were unequally elevated and depressed. In Southern Kentucky and 
Tennessee the Upper Silurian and Devonian rocks run out to feather- 
edges on its sides, while they cover its summit in Logan county, Ohio, at 
an altitude now more than a thousand feet higher. This proves that 
during the Upper Silurian and Devonian ages, the southern portion of 
the arch was much higher than the northern. This condition of things 
was, however, reversed in the Carboniferous age, for in Southern Ken- 
tucky the Carboniferous Sea swept entirely over the arch, and the Lower 
Carboniferous limestone and Waverly rocks accumulated on it te the 
depth of more than five hundred feet, while in Ohio the Lower Carbon- 
iferous limestone scarcely reached its base, and the Waverly rocks did not 
cover its summit. | 
In the Coal Measure epoch, the Cincinnati arch was apparently a land 
area throughout its entire length, its northern end being then, as now, 
its highest portion, and connected with the highlands of Canada. This 
is conclusively proven by the manner in which the Coal Measure strata 
terminate on the western margin of the basin in Knox and Richland 
counties, where the coal-beds abut against pre-existent Waverly hills. 
THE CINCINNATI ‘GROUP. 
In Chapter IV of Volume ! of this report, the relations of the Cincin- 
- nati Group are discussed at some length, and it is there shown by con- 
clusive evidence that the Lower Silurian limestones exposed at Cincin- 
nati are not, as has been claimed, the equivalents ef the Hudson River 
Group of New York, but that they represent the entire Trenton lime- 
stone’ series. : 
In the chapter referred to, a partial list was given of the Lower Silur- 
ian fossils which are found in Ohio, Canada, New York, and Tennessee, 
and it was shown from this list that the Cincinnati Group contains not 
only the characteristic fossils of the Hudson River Group, but a still 
larger number of those which occur in the Trenton limestone in New 
York and Canada, and even some of those of the Black River and Birds- 
eye limestone; and these are all so intermingled as to make it impossible 
to identify any one of the subdivisions of the Cincinnati Group with 
either of the Lower Silurian limestones of the east. 
