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, wc deem it a valua¬ 
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, however, to connect our observa¬ 
tions together so as to be satisfied that such is the fact, or that it does 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, be referred to the Catskill division. 
The great body of materials forming 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 
than is implied in the old name by which this rock has been distinguished. 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 the 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, hut 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 the 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 tire base, especially on the eastern slope, 
the dip is quite 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. 18G. 
