36 PALjEONTOLOGY of NEW-YORK. 



Scarcely one of the fossils here described is known to ascend into any of the subsequent 

 depositions. Of the peculiar forms presented, and which began and terminated their 

 existence with this mass, we may mention the Maclurea, Scalites and Raphistoma, 

 of which generic analogues are scarcely known in a higher position. We may cite also 

 two species of Bucania, which are remarkable and well-characterized shells, neither of 

 which appear in a higher position. There are at least two species of Orthoceras unknown 

 elsewhere, besides a considerable number of less prominent species figured on Plates IV. 

 and IV. (bis). 



We therefore feel warranted in imiting the several strata, as seen at Chazy, Galway, 

 He la Motte and other places, as a group, marked by a peculiar assemblage of fossils, and 

 as much entitled to this consideration as any other. In the Mohawk valley, as before shown, 

 we do not find a full development of these strata ; the Calciferous sandstone is often suc- 

 ceeded directly by the Birdseye limestone, or there are a few calcareous layers between 

 them. In some localities along this valley, these interposed calcareous layers assume a more 

 definite character, approaching to the oolitic portions of the Chazy limestone. In such 

 localities they contain fossils, one or two of which are apparently identical with those of the 

 Chazy limestone at Chazy, and others which have not been observed at the latter locality. 

 The small fossil shells, Ophileta, figured on Plate III., hold this position, and may probably 

 be referred to the period of the Chazy limestone, though, in the locality where they occur, 

 it is impossible to separate the layers containing them from the Calciferous sandstone. 



The thinning out of the materials constituting this rock or group of strata, in the Mohawk 

 valley, leaves the Calciferous sandstone and the succeeding Birdseye limestone in contact ; 

 bringing into direct succession, in numerous places, the fossils figured on Plates I. and III. 

 with those of Plates VIII. and IX., those of the intermediate plates rarely or never appearing 

 along the Mohawk valley. These remarks will enable the student to iniderstand the absence 

 of many peculiar fossils from a large extent of country in Central and Southern New-York, 

 as well as in localities farther southwest. 



