II2 
BULLETIN OF THE LABORATORIES 
tions during the Hamilton period over the entire area considered — in- 
deed a much more extensive one. The change which made the sedi- 
ments of New York littoral sands and induced a modification of fauna 
may not have been felt at once in distant areas in Ohio. The undis- 
turbed seas in Ohio may have been concealing a fauna closely allied 
to the Hamilton, while the oscillation along the western border of the 
Chemung area may have once and again thrown a great apron of its 
own sediments over Hamilton beds, only to be in turn covered by a 
similar apron from the Ohio ocean. 
What, indeed, is to prevent us from believing that when the early 
fluctuation of the north-eastern part of this area was bringing more and 
more of the Silurian shore-line within its own erosive power and ac- 
cumulating coarse detrital material in great masses, the weedy sea of 
the Hamilton continued unaltered in Ohio. Sandy bottom, stormy 
waves and unaccustomed conditions of all kinds must have their effect 
on the organization of the fauna and, if accepted ideas of the causes 
of evolution are correct, a sudden change would be seen in a faunal 
development more or less forced, one-sided, and local. 
Great variety within narrow groups is the rule under such condi- 
tions. Just as the sudden formation of a prairie out of a morass de- 
velops hundreds of species in a few genera, so, in this case, such 
groups as could cope successfully with the new conditions would ex- 
pand while others disappear. As the agitation extended westward 
the plot thickens. Somewhere on the western part of our area we 
should expect to find strata strangely interblended, just as a player in 
cutting and shuffling a pack thrusts the edges of the cards between 
each other. Here we should find a stratum marking the return of the 
former conditions. 
Such a state of things as we have supposed would explain the 
conditions in northern Ohio in the period before the Berea grit, which 
put an end to all this by calling in the agency of shore action on its 
own account in the western part of the basin. Of this there is abund- 
ant evidence in the oblique lamellation and fucoids of that horizon. If 
we admit the probability that Hamilton arid New York Chemung 
played a game of hide and seek during the preliminary oscillation they 
certainly were sadly disturbed during the Berea epoch. 
Then followed a gradual depression with occasional infiltration 
from the Chemung area, now rapidly contracting. The Berea shales 
mark the long period of isolation and gradual depression. When the 
