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[Assembly 
water in motion which might transport from different directions the two 
materials of the rock. This group -appears to have been deposited from 
an ocean alternately at rest, and disturbed. Thick masses of sandy 
shale occur, bearing ripple marks through their whole depth;- these are 
succeeded by others of variable thickness, without ripple marks, and 
having the faces smooth and plain. Numerous alternations of this 
kind have been noticed through many hundred feet. Fossils never ac- 
company the rippled layers, but are invariably found with the smooth. 
The materials of the two differ very slightly in mineral composition, the 
rippled ones being more sandy. The absence of fossils in the latter may be 
explained, by supposing the unquiet state of water during the deposition 
of the rippled shale to have been unfavorable to the development of or- 
ganic life. So far as I have observed in this and other localities, the 
greatest accumulation of fossils is always accompanied by fewest ripple 
marks. 
The changeful state of our planet at that period may have occasioned 
numerous risings and sinkings of the crust, some portions of which may 
have been disturbed oftener than others; one undergoing the oscillatory 
movement while another was at rest. This may be considered proved 
from the fact that undulations are exhibited in some localities, while a 
distance of a few miles shows a plane and undisturbed surface. Thus 
the undulations of the rocks on Seneca lake have not been communica- 
ted to those on the western shore of Crooked lake; although the latter 
are part of the same mass, separated only by a distance of ten or twelve 
miles. The valley of Crooked lake could have had no influence in in- 
terrupting the motive force, as probably at that time it was not excava- 
ted; and farther south we find other undulations oi which the counter- 
parts are exhibited on each side of the valley. 
These uplifting movements would form bays, or protect certain por- 
tions of the sea where animals might exist in great numbers, while every 
other part for miles in extent, were too unquiet for the development of 
preservation of animal life. 
In numerous localities of these rocks, the edges of strata, when ex- 
posed in ravines and other places, are found covered with crystals of 
sulphate of lime. This circumstance is by no means universal among 
the shales below, although observed in some localities: while in the pre- 
sent group there are few exceptions. Pyrites, in minute particles, is 
every where disseminated, decomposing on exposure, and hastening the 
destruction of the rocks; while the sulphuric acid combines with the mi- 
