INTRODUCTION. 
9 
the Calciferous sandstone. Thus in place of limestones, we have a wide¬ 
spread arenaceous deposit, destitute of organic remains. This later deposit 
of sandstone in the northwest, though usually no more than from fifty to 
eighty feet in thickness, becomes of extreme interest in considering the 
physical conditions there existing. While the ocean in its eastern extension 
was in a quiescent state, and inhabited by numerous forms of animal life, 
the same ocean a thousand miles westward was the scene of disturbances 
which abraded the arenaceous materials of an ancient land, and spread 
them eastwardly over its bed. 
We would naturally infer that the deposits of the same age on the 
eastern side of the ancient ocean would bear some traces of disturbances 
so great as those which were taking place on the west; and accordingly 
we find that in the midst of the Chazy limestone there is intercalated a 
thin bed of light-colored sandstone, and there are likewise some more 
argillaceous bands charged with numerous marine plants. 
If our conclusions regarding the equivalency of these two formations 
be correct, we have at one extremity of this oceanic area a destitution of 
organic remains, while at the other, life was abundant, except for a short 
period, when the influx of arenaceous and argillaceous material degraded 
the conditions below those required for the support of animal life. 
The section of these beds, as they occur in Missouri, does not show any 
sandstone immediately succeeding the Calciferous sandstone, as in the 
States north of it; but, on the contrary, that rock is here followed directly 
by the Birdseye and Black-river limestones. The absence of the Chazy 
limestone is also distinctly shown in the section given in the Missouri 
Report. 
While these investigations in the north and west are bringing to light 
new forms of this ancient fauna, we learn that the Paradoxides harlani 
has been rediscovered in the ancient metamorphic slates of Eastern 
Massachusetts, in a part of the country from which no fossils have here¬ 
tofore been obtained. Although we do not yet know the precise equivalency 
of these slates, we have some reason to place them in the same horizon 
[ Paleontology III.] 2 
