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 

 go 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 oorrect, 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 Missoiu-i, 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 

 [ Pal^bontoloot III.] 2 



