NIAGARA GROUP. 



107 



be recognized ; but it contains few fossils, and has so far thinned out as to be quite unimpor- 

 tant. Still, however, when we come to the base of the Helderberg mountains, we find a mass 

 ~ of limestone about four feet in thickness, holding the place of the Niagara limestone, and 

 containing many similar fossils*. 



In the town of Verona, there are two or three localities where the limestone, with a con- 

 cretionary shale below, may be seen resting upon the rocks of the Clinton group. Still farther 

 cast, in the vicinity of Clinton village, and between this place and New-Hartford, there are 

 many loose masses of concretionary and fragmentary limestone lying along the road ; these 

 belong to a thin band of limestone of the same character, which is the only representative of 

 the group. 



At one point on Steele's creek in Herkimer county, may be seen this thin band of limestone, 

 representing the Niagara group ; but to the eastward of this point, for many miles, we have 

 thus far been unable to find any evidences of its existence. 



In localities west of New- York, this group becomes almost entirely calcareous, and forms 

 a distinct thick mass of limestone bearing the lead ores of Wisconsin, Illinois, Iowa, &c. In 

 this part of the country it often produces a distinct topographical feature, and on the Missis- 

 sippi river is equally conspicuous with the great Carboniferous limestone. In this western 

 extension of the limestone, we already know many fossils which have not been seen in the 

 same rock in New-York. 



In the western part of New-York, the lithological characters of the Clinton and Niagara 

 groups are so similar that they could well be united. The fossils also of the two groups, though 

 generally distinct, are nevertheless generically similar, and several species pass from the lower 

 to the higher group. The upper limestone of the Clinton group, which forms a strong line of 

 demarcation between the two, contains in its western extension several fossils usually re- 

 garded as peculiar to the Niagara group. Among these may be noticed the Caryocrinus 

 ornatus and the Hypanthocrinus decorus. It can not be denied, therefore, that there is a 

 gradual approximation in the two groups, both in lithological and palceozoic characters, as we 

 trace them westward within the limits of the State of New-York. Still farther west, the assimi- 

 lation becomes more perfect, and there appears to be no line of separation between the two 

 groups. At the same time the fossils appear to be commingled ; for, in several collections 

 sent me from Wisconsin and other places, fossils, which in New-York are restricted to their 

 respective groups, are here collected from, and referred to, a single rock. This fact is not at all 

 surprising, if we consider the gradual change which takes place in western New- York, and 

 which has been described in the Report on the Fourth Geological District. 



On the other hand, when we examine the Clinton group as it is developed in central New- 

 York, it seems impossible to assimilate in any degree its discordant and protean masses, with 



♦I have not united the fossils of this limestone with those of the Niagara limestone, though satisfied as to its posi- 

 tion, but have described them under the head of "coralline limestone," the name by which this mass has long 

 been distinguished in the neighborhood of Schoharie. In this manner these fossils follow those of the Niagara lime- 

 stone in the descriptions, but it is not intended to be understood that they belong to a higher position. 



