NIAGARA AND LOWER HELDERBERG GROUPS. 123 



carded as having no separate or distinct existence in the series ; 

 bnt the science of geology, and those who pursue that science, 

 have an interest in this question far superior to one of mere 

 personality. 



Geological relations and geographical extension of the groups 



in question. 



Starting from the typical locality of the Niagara group, 

 where, of the shale and limestone, we have a thickness of some- 

 thing more than two hundred feet, and tracing the outcrop in 

 an easterly direction, we find a very gradual but pretty con- 

 stant thinning of the bed's of the formation, so that at a point 

 one hundred miles east of the Niagara river it has a thickness 

 of scarcely one hundred feet. Farther east, in Oneida county, 

 the formation is still thinner, and in some places has become 

 in part or almost entirely a brecciated and concretionary mass, 

 with few or no fossils.* 



Going eastward it becomes still further attenuated, but can 

 still be traced both in its physical aspect and outcrop, and by 

 its fossil contents. In the neighborhood of Schoharie, Coble- 

 skill, Cherry galley, etc., it is known as the Coralline Lime- 

 stone, from its abundance of corals. These are principally 

 identical with the corals of the Niagara group in western New 

 York ; and most of the species of Brachiopoda, which occur in 

 a condition to be recognized, are similar or identical with Niag- 

 ara forms, while there are several species quite distinct from 

 those of the Niagara group in the west. The upper limit of 

 Halysites catenulatus, so far as known in New York, is in 

 the Niagara limestone ; and this fossil occurs in the coral- 

 line limestone at Schoharie and at Litchfield, in Herkimer 

 county. 



I have given in vol. ii, Pal. N. Y., p. 321, more at length my 

 reasons for regarding this coralline limestone as the easterly 

 continuation of the Niagara group ; and since the time of that 

 publication I have made numerous observations upon the 



* In that part of the State the formation is so insignificant, that it was origiE 

 ally regarded by Mr. Vanuxem as a subordinate member of the Protean or Clin- 

 ton group ; and was only recognized by him as a distinct formation in 1839 ; after 

 the investigations in the western counties bad shown its true relations and im- 

 portance. 



