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Association of American Geologists and Naturalists. 159 
oped in Ohio, Indiana and Kentucky, and also on the Mississippi. The 
general character remains the same, with the exception of being light- 
er colored—the fossils are identical. 
Then come the Marcellus shales and the Hamilton group, which form 
an important part of the series in New York. Its thickness is nearly 
a thousand feet, and contains more individual fossils than all the rocks 
below them. In the eastern part of this state these groups consist of 
slaty and sandy shales and impure sandstone—westwardly, the sand di- 
minishes and the mud inereases. In Ohio, &c. the lower member alone, 
a black shale, is visible, and it has thinned down to one hundred or even 
fifty feet, and has apparently lost all its fossils. Here we have a bet- 
ter instance of the gradual change and final disappearance of fossils 
than is elsewhere afforded. The lithological characters also change as 
we proceed west, and in accordance with the laws of mechanical de- 
posits. If the origin of the deposit was at the east, we have first the 
sand—then mud intermingled with sand—then mud alone, and beyond, 
the clear blue ocean without turbidness. 
We may then infer, that in this great ocean, greater depth and quiet 
were found at the west, and at the east a shallower sea and proximity to 
Jand ; and we have here exhibited the influence of the conditions men- 
tioned at the beginning of this paper. With slight exceptions all the 
intermediate deposits to the Old Red Sandstone may be considered as 
one group, made up of shales, with thin alternating sandy layers and 
flagstones. Going westwardly the shale increases and the thickness di- 
minishes. In the centre of this state it has reached its maximum. - 
And in these also the same change in the character of the fossils is ev- 
ident as in that below. Large numbers of Fucoides continue in this 
sroup for a great extent. In Ohio, this group has diminished from two 
thousand in New York, to four or five hundred feet in thickness, and 
there is even a greater diminution of its fossils; and this gradual de- 
crease of thickness and number of fossils continues, so that in Indiana 
it is almost non-fossiliferous. Here terminates the New York system, 
the rocks of which attain a greater development than perhaps in any 
part of the world. (Mr. Vanuxem thought the Old Red Sandstone 
should not be excluded from the system of New York rocks.) 
We see, then, uniformity of lithological character in the calcareous 
formations is accompanied by uniformity of fossils, and vice versa ; 
and that a change in mechanical deposits at different distances from 
their sources is also attended with change in the fossils. We find too, 
in the first period, which includes the Hudson river group, a higher de- 
sree of vitality over the west portion; and in the second, that of the 
calcareous deposits an organization more fully developed here at the 
