154 HELDERBERG DIVISION. 



3. A gray impure limestone, in which there are numerous small irregular-shaped cavities or cells, 



nbling those of lava or amygdaloid. These beds are associated with the above. 



4. Thin-bedded shaly limestone, passing upwards into a fine-grained one whose thickness has increased: 



this limestone emits a ringing sound when struck. These beds constitute the Manlius waterlime 

 series of the Reports. 



It is proper to observe here in regard to tliis last division, which is a deviation from the 

 reports, that there seems to be a gradual passage upwards, from the thin-bedded fragile 

 shales and shaly limestone-, to the thicker and firmer beds of the last division. There is 

 DO wi 11 marked line of divison between the lower and upper masses of the group, as defined 

 above. The Pentamerus limestone, which succeeds the waterlimes, is clearly a different 

 rock. Below, the Niagara limestone is a very distinct deposit in all respects ; but when we 

 once pass into the Onondaga-salt group, no characteristic lines can be discovered, which 

 seem to be suitable to the purpose of serving as lines of demarkation. Then again it is our 

 wish to diminish the number of groups, as far as possible, without doing violence to ar- 

 rangements founded in nature. 



I shall now proceed to speak in detail of the division which I have just proposed. 



1. Red shale. 



The ground color of this mass is a blood-red, npon which patches of green are common ; 

 and sometimes or in some parts of it there are strata winch are entirely green, a red shale 

 alternating to a limited extent with green. The true character of these beds is so much 

 concealed by their own debris, that it is often unnoticed. The rock is extremely fragile, 

 and is constantly breaking down by the action of the weather : hence the surfaces exposed 

 look more like a marl bed than a solid rock. The fracture is earthy, and the divisions 

 which usually mark the strata are obscure, if not entirely absent. 



Localities where this rock is exposed. As has been stated in regard to the commencement 

 of the Clinton group, this rock too does not appear east of Herkimer county. At Steel's 

 creek, at Cruger's mill, and between Mohawk village and Dennison's on the Saiujuoit 

 creek, on the north and west side of Paris hill, the red shale crops out, and appears under 

 the characters winch have been given above. Farther west, but still in Oneida county, 

 the rock appears near Hamilton College ; from which place, it spreads out and extends 

 into Madison county, in the eastern part of which it is cut through by ibe Erie canal. In 

 us western prolongation into Onondaga and Cayuga counties, it forms a band to the north, 

 but it runs nearly parallel with the Canal. Still farther west and in the vicinity of 

 Genesee river at Rochester, the rock exists but obscurely. It was excavated in a well in 

 Brighton, four miles south of Rochester. Mr. Hall expresses some doubts of its con- 

 tinuance farther west than this river, unless indeed the character of the rock is changed. 



Thickness of the red shale. Mr. Vanuxem estimates its thickness in some places at five 

 hundred feet, or as varying from one to five hundred feet. On the West branch of Steel's 

 creek, it forms a mass, in a precipice or perpendicular cliff, eighty feet thick. 



