82 GEOLOGY OF OHIO. 
Waverly group have been a fruitful source of discussion for many years, 
a discussion which, as will be shown further on, we have been able to 
bring to a conclusion by demonstrating that this is an integral portion 
of the Carboniferous system. The relations of the Waverly to the Cats- 
kill and Chemung rocks are, however, not yet accurately determined, 
and it is plain to see that it will not be easy to harmonize views on this 
subject. As I have suggested in the geological portion of Volume I., we 
have, at what 1s now regarded as the base of the Carboniferous system, a 
ereat mass of mechanical sediments—the Waverly group. This is the 
lowest member of a trinity of deposits—the Carboniferous limestone 
being the central, the Coal Measures the upper member. These form 
one of the great circles of deposition which compose all the systems of 
sedimentary rocks, each of which is the product of a distinct invasion of 
the continent by the ocean. But the Waverly sandstone series is under- 
lain by the Catskill, the Chemung, and the upper half of the Portage 
group, which also form a mass of mechanical sediments. Much more 
study of this group of strata will be required before their relations to 
each other, or to the rocks above, can be accurately determined. As I 
have remarked elsewhere, the Gardeau and Cashaqua shales of the Por- 
tage group have nothing in common with the Portage sandstones above, 
while their lithological and zoological affinities with the Hamilton 
below are such that they should be properly united with that formation. 
I have also suggested that since a great physical change occurred at the 
epoch of the deposition of the Portage sandstones—and this was appar- 
ently the beginning of a new geological cycle, and one of which the Car- 
boniferous age was the continuation—the Portage sandstone might be 
with propriety considered the base of the Carboniferous series. This 
proposition was made not for the purpose of harmonizing the facts with 
a preconceived theory of circles of deposition, but because both the phy- 
sical and zoological evidence favor the union. The physical evidence is 
much in itself, since all the great material changes through which our 
continent has passed—of elevation, of depression, of heat and cold, alter- 
nations of land, and shore, and sea—have left lithological records which, 
if carefully studied, will be found to be as legible and reliable as those 
formed by organic remains. Indeed, the two histories are not only har- 
monious, but are so interdependent that each is indispensable to the 
proper understanding of the other. 
The significance of the sequence of sediments which is. observable in 
what I have termed circles of deposition, is such that no one can be blind to 
it and yet read correctly the history of our stratified rocks. The molluscous 
fauna of the Chemung is much more closely allied to that of the Carbonifer- 
