ONONDAGA-SALT GROUP. 161 



series, the thin shaly beds, which in Onondaga county contain gypsum and the hopper- 

 form cavities, arc certainly wanting, and they have not been recognized in this part of the 

 State. They ought not, it is true, to be found at the falls of the Rondout, if the series 

 consists only of the Clinton and Niagara groups ; the former comprising the shales, green, 

 red and mottled, and the ten feet of sandstone ; and the latter, the limestone at the head 

 of the falls, which is quarried for cement. The plaster beds in this case ought to be found 

 above the falls, resting upon the cement rock or the Niagara limestone. 



The waterlimea are also exposed on the eastern outcrop of the Helderberg, on a range 

 not far west of the Hudson river, near the villages of Kingston, Saugerties, Catskill, 

 Leeds, Coxsackie, Coeymans, New-Baltimore, and also on the east side of Hudson river 

 at Becraft's mountain. At all these localities, the upper beds are the ones which are 

 exposed, and which are ranked rather as thin-bedded limestones than as shales, the latter 

 being always disposed to disintegrate rapidly, and pass into the condition of soil. 



Other parts of the Helderberg range also furnish important points of exposure : thus, 

 about one and a half or two miles east of New-Scotland in Albany county, the same series 

 of beds appear ; and these may be traced around on the northern outcrop, or rather ter- 

 minus of the Helderberg range, as far as Schoharie. Still onwards through Carlisle, 

 Cherry-valley, Springfield, Warren, and through Oneida and Herkimer counties, they 

 maintain much the same character. In Onondaga county, the lower part, and that which 

 crops out in the village of Manlius, is shaly, and green or drab-colored, with cavities lined 

 with crystals of lime. This part can not be distinguished from that at the falls of the Ron- 

 dout, of which I have expressed some doubts whether it is to be regarded as belonging to 

 the Watevliine series or the Clinton group. 



In Onondaga county, the series terminates abruptly above ; a fact of considerable im- 

 portance in fixing the limits of the series, as the circumstances show that an important 

 change took place in the condition of the seas in which these rocks were in the progress of 

 formation. 



At Manlius, the exposed rocks are as follow : 



1. Greenish shales with imperfect geodes, fragile, and rapidly decomposing: exposed in the road above 



the village. 



2. Thin-bedded limestone, which becomes of a drab color on exposure to the weather. 



3. Compact black thick-bedded limestone, much broken, in thin beds, from eight to ten feet thick. 



4. This is succeeded by a lighter colored limestone, eight feet : this last supports a few feet of the 



Pentamerus limestone, which is quite concretionary. 

 The mass which is burnt and used for hydraulic cement, is the upper four feet of the drab- 

 colored No. 2, and just beneath the black compact limestone. It is a mass thicker bedded 

 than the lower part of the same tier, from which it is not very easy to distinguish it. 



At Auburn, the quarries north from the town give nearly the same series. The black 

 rock, with a small univalve, occurs in great abundance at both places. 



In Monroe county, Mr. Hall gives a section at West-Mendon, consisting of the Onon- 

 daga salt group, twenty-five feet, in thin courses of light drab or ashen hue, succeeded 

 [Agricultural Report.] 21 



