TACONIC QUESTION IN GEOLOGY. 229 
ferous shales measured in Blair county between the limestone below and the overlying 
sandstone, we find not less than 6,000 feet of unfossiliferous strata. As lone since mea- 
sured by Rogers, on the west side of the Delaware River at the Water-gap, there are 6,102 
feet between the base of the sandstone No. IV. and the underlying Auroral limestone.* 
Mr. Chance, ina later section in this vicinity, makes them above 3,900 feet, and Lesley con- 
cludes from observations on the Susquehanna that they have an ageregate thickness of not 
less than 6,000 feet, which agrees with the early measurements of Rogers. The characters 
of this great group of strata in the Kittatinny valley, included both by Rogers and by the 
second geological survey, in the Matinal division are exceedingly variable, and they pre- 
sent important local differences. The roofing-slates already mentioned ( 20) are confined 
to a small area in the north-west part of this valley, occupying a narrow zone lying from 
one to three miles south from the base of the Kittatinny Mountain, and extending from a 
point in New Jersey a few miles east of the Delaware Water-gap, across the Delaware and 
Lehigh, and a few miles west of the latter river. These roofing-slates were assigned by 
Rogers to the lower part of the group in question. According to Chance also, who has | 
lately examined them, they are very low in the series, and of no great thickness ; but are 
affected by such sharp flexures that the dips on both sides of the anticlinals and synclinals 
are nearly parallel, so that the apparent thickness of the roofing-slates is much augmented.f 
In the region to the west of the Lehigh, in the counties of Berks and Lebanon, these 
Matinal slates include a great amount of coarse arenaceous rock, and rise into bold hills. 
Some parts consist of heavy grey sandstones with conglomerates, and bluish or greyish 
shales with thin-bedded limestones. Large portions are characterized by a predominant 
reddish or reddish-brown color, with interstratified beds of yellow or fawn-colored shales, 
and are said by Rogers to resemble the strata of the Medina and Clinton, above No. IV. 
Mention should also here be made of the existence of considerable masses of conglo- 
merate made up of more or less completely worn pebbles of the Auroral limestone in a 
calcareous cement, which are found at several points in the great valley, and have been 
described by Rogers as resting upon the Auroral limestone.f 
§ 30. From my observations in this region, in 1875, when I had an opportunity of 
seeing the rocks of this group at several points in the Appalachian valley between the 
Lehigh and Schuylkill rivers, I was struck with their great resemblance to the First 
Graywacke of Eaton (the Upper Taconic of Emmons, or Quebec group), as seen from 
the banks of the St. Lawrence at Quebec, to the valley of the Hudson ; which, it will 
be remembered, was, by Mather, confounded with the Second Graywacke (§ 12). It is 
apparent from a section to be seen a little west of the Lehigh, below Slatington, that the 
coarse red and grey sandstones, with red shales and conglomerates, overlie the roofing- 
slates of the valley; and their geographical relations are such as to suggest an uncon- 
formable superposition. 
§ 31. Regarding the rocks of this valley, I expressed, in 1878, my belief “that besides 
the Auroral limestones, with their succeeding argillites, and the unconformably superim- 
posed (Oneida) Silurian conglomerates of the North Mountain, there are, to the west of 

* Second Annual Report, 1838, p. 35. 
+ Rogers, Geology of Pennsylvania, I. 247 ; also Second Geol. Survey Penn, Report G, 6 ; pp. 340, 363, 
t Geology of Pennsylvania, I., 252: 
