194 CATSKILL DIVISION. 



characteristic of this part of the New-York series. Certainly it is not observed in any of the 

 lower rocks ; and as it is a very constant mass, and widely extended, we deem it a vahia- 

 ble wayboard by which position may be determined with a good degree of certainty. This 

 mass, too, it may be important to say, is regarded by Mr. Vanuxem as equivalent to the 

 cornstone of the Old Red sandstone.* It appears quite early among the strata, and goes 

 up to the middle of the series. We have not been able, liowever, to connect our observa- 

 tions together so as to be satisfied that such is the fact, or that it docs not extend farther than 

 the central part of the rock. We believe it belongs to the inferior part, and may be sought 

 for the purpose of identifying this part of the group. The diagonal stratification is another 

 peculiarity of the rock, which has been referred to already. It is spoken of by Mr. Hall, 

 as appearing in the upper part of the Chemung group. The difficulty, in New-York, of 

 defining the limits of groups, is such that it can not always be made clear where one begins 

 and another ends. Hence it may be true that this part of the so called Chemung group 

 might, with great propriety, l^e referred to the Catskill division. 



The great body of materials fornu'ng the Catskill division, are grits, alternating fre- 

 quently with olive-colored shales, red slate, or red marl. The latter is sometimes from 

 thirty to fifty feet thick ; yet there is less of red rock than is generally supposed,, or less 

 tlian is implied in the old name by which this rock has been distinguislied. The name 

 Old Red sandstone, or Red system, would lead to the inference that it is a red rock mainly ; 

 whereas only about one-third of it is red, the rest being a dark slate, or greenish or grayish 

 flagstone. Originally the color of tlie slate was olive or green, throughout the series of 

 beds : it is by atmospheric action that the slates and shales have changed their primitive 

 color. This process is still in progress ; and the darkish green rocks, on breaking down, 

 assume first a brownish tint, and then a red one, capable of staining substances with the 

 same color, an effect due to a change in the oxide of iron, which in the green slates is a 

 protoxide, but by a further acquisition of oxygen becomes the peroxide. 



The engraving on page 192 is a view of the Schoharie creek at Gilboa, on the road from 

 the village leading to tlie Manorkill falls : it looks south. All the ranges which close in 

 upon the creek, and bound its valley, belong to the Devonian system. 



Dip and stratification of this series. To the eye within a distance of a few feet, the rocks 

 appear horizontal ; but when viewed at a considerable distance, or from a point where 

 there is a sufficient range, they indicate a dip to the southwest, less, however, than the New- 

 York rocks are known to exhibit at distant points ; yet this remark applies to the series 

 which form the body of the Catskill mountains. At the base, especially on the eastern slope, 

 the dip is {juite steep ; at least it is decidedly marked even in the outcrop of the cliffs which 

 terminate the successive terraces. The stratification is no less regular than the dip : at the 

 base, the strata are parallel ; at the middle, and towards the summit, the diagonal stratifi- 

 cation is common. 



• Vanuxem's Report, p. 180, 



