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297 
would otherwise effect. Almost all the ravines where this shale is ex- 
posed, appear to have formerly been large water courses, the present 
streams cutting a narrow channel in the hottom^ composed sometimes to 
great depth of water worn fragments of shale, and the rocks above, and 
covered with soil supporting the largest forest trees. Along the banks 
of the ravines, the destruction of the shale has produced a thin but rich 
soil, which, though the rains are constantly washing it down into the 
valleys below, produces a small growth of trees, and a luxuriant one of 
flowers, of which a greater variety and in greater beauty, can scarcely 
be seen. The family of Trillium, the Corydalis, Dentaria, Caulophyl- 
lum, Tiarella, and the delicate Mitella, with hundreds of others, spring 
up in the greatest perfection and profusion. As beautiful objects of 
natural scenery, these ravines cannot be surpassed. 
IV. Olive shale. Succeeding the compact calcareous shale, is a more 
fissile, bluish or olive shale, often containing small nodules or concre- 
tions like the claystones, or concretions in common clay: the lower por- 
tion of the mass is highly calcareous, partaking of the character of that 
below; it readily crumbles on exposure to the weather, producing a fer- 
tile soil. Above this it becomes gradually more fissile, and of a darker 
colour, and the fossils gradually diminish, and finally almost entirely dis- 
appear. In this rock, for the first time among the shales now describ- 
ed, we meet with a finely striated species of Orthis, which occurs in 
the Rochester shale. Circumstances, however, appear to have been 
more favorable to its development here than there, as it appears in much 
greater numbers, and twice the size of the same in the Rochester shale. 
Another fossil which existed at the time of the deposition of the Ro- 
chester shale, again makes its appearance about this period. Trilobites, 
which are extremely rare in any of the lower shales of this series, be- 
gin to appear here, and attain their maximum a few hundred feet higher. 
The upper part of this shale becomes of an olive colour, and sepa- 
rates readily into thin laminae, which are deeply stained with manga- 
nese; it contains few fossils, and those noticed, were fragments of Or- 
thocera. 
This rock may be examined to advantage a few miles south of Ty- 
ler's tavern, on the Seneca lake shore, for several miles, though in many 
places, from its ready destructibility, it is broken down and covered with 
alluvium. On the Cayuga lake shore, the shale can be examined near 
Shelldrake point, and along the ravine in the neighborhood. The fos- 
[Assera. No, 275.J 38 
