C. Callaicay — L. Helderherg Group of N. York. 273 



the Lower Helderberg group occupies the chief space between the 



Cambro-Silurian and the Upper Heklerberg, and this holds good also 



of the Niagara group in the west. The following section will explain" 



this misconception, and at the same time show the true relation of 



the deposits in question. 



Section 3. 

 Eastern New York. Western New York. 



7. Upper Helderberg Group. 

 6. Lower do. do. 



5. Water-lime Group. 

 4. Niag-ara „ 



3. Clinton Group. 

 2. Medina Sandstone, 

 1. Hudson River Group. 



This section is about 200 miles from east to west. Being drawn 

 from memory, it does not pretend to be an accurate representation of 

 the comparative thickness of the beds. It shows the relations of the 

 groups, with an approximation to the thickness, which is all my 

 purpose requires. It will be seen that the Hudson Eiver shales and 

 slates form the basis of the whole succession. The Medina Sand- 

 stone is a considerable formation on the Niagara and Genesee Kivers, 

 but thins out towards the middle of the State. The Clinton Lime- 

 stone and Shales are in force in the same localities, but to the east, 

 in the Helderbergs, it has thinned out to a shale of seven or eight 

 feet in thickness. The Niagara Limestone and Shale thin out in the 

 same direction, and are represented at Schoharie by two or three feet 

 of coralline limestone. The Saliferous or Water-lime group is per- 

 sistent in varying thickness from west to east.- The succeeding 

 Lower Helderberg rocks, however, are the converse of the preceding ; 

 and, from a thickness of over 200 feet in the east, thin out entirely 

 towards the western side of the State. The limestone capping of the 

 Upper Helderberg series extends in an unbroken band from east to 

 west, overlapping the Lower Helderberg on to the Water-lime, and, 

 beyond the western boundaries of the State, oveilapping the Water- 

 lime on to the Niagara Limestone itself. This section, if accurate, 

 decides the question ; and of its accuracy I have no doubt. I have 

 made numerous traverses across it in both eastei'n and western New 

 York. I have, furthermore, the unimpeachable testimony of Professor 

 James Hall to the effect that he has traced the several formations 

 from east to west, and he has assured me in repeated conversations 

 that the section is substantially as I have represented it. The Lower 

 Helderberg group, therefore, clearly overlies rocks of the Niagara 

 period. It is also distinctly separated from the Niagara by the charac- 

 ter of its fauna. The only species known to me as common to the 

 two formations are Atrypa reticularis and Stroplwmena rhomhoidaUs. 

 Of these A. reticularis ranges from Middle Silurian to the Carbon- 

 iferous, and S. rhomhoidaUs from Lower Silurian to the Carboniferous, 

 so that their testimony does not in the slightest degree militate against 

 my position. This evidence is very decisive, when we remember that 



DECADE II. VOL. V. — NO. VI. 



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