TACONIC QUESTION IN GEOLOGY. 225 
ponding to that already described as occurring in the Central district of New York, (§ 13) 
and to what is seen along the north shore of Lake Ontario, in Canada. A similar condition 
of things occurs in the Nippenose, the Nittany, and the other so-called coves or limestone- 
valleys, which are found in central Pennsylvania, and like that of Kishacoquillas, are eroded 
anticlinals. Accounts of these will be found -in Rogers’s Geology of Pennsylvania, 
Vol. I. pp. 460-511; and also in Report T., on Blair county, by Franklin Platt, of the 
second geological survey of the state. The latter tells us that “there is no appearance of 
non-conformability here between III. and IV ;” that is to say between the Loraine shale 
and the succeeding Oneida-Medina sandstones. Within these valleys, there appears 
beneath the fossiliferous limestone, a great mass of magnesian limestones, several thousand 
feet in thickness, abounding in ores of iron and of zine, and identical with the limestones 
of the Appalachian valley. 
§ 20. When we pass from the central region of Pennsylvania to the east of the North 
or Kittatinny Mountain, we find, along the western borders of the Appalachian valley, the 
sandstone, No. IV. which constitutes this monoclinal ridge, resting upon a great series of 
schistose rocks, declared by Vanuxem to belong to the Frankfort or lower division of 
his Hudson-River group, in which he included the roofing-slates of the region. The con- 
tact between the’ overlying sandstone and these rocks is not, however, as in the central 
valleys, one of conformable passage, through intercalations, into an underlying series of 
fossiliferous shales, but, as may be observed at the Lehigh Water-gap, one of non- 
conformity. 
H. D. Rogers noted the fact that the conglomerates of the sandstone No. IV., here 
include “many rounded pebbles and fragments of the three underlying formations which 
intervene between it and the Primary rocks at the bottom of the series.”’* He recognized 
among the pebbles portions of the Primal sandstone, of chert derived from the Auroral 
limestone, and of the Matinal slates. The presence of all these, which I have verified, 
is sufficient to show the complete stratigraphical break which here separates this Silurian 
sandstone from the subjacent argillites. These are seen along the banks of the Lehigh, resting 
in apparent conformity upon the Auroral limestone; which, with its overlying and 
interstratified schists, and its subjacent quartzite, makes up the Lower Taconic of Emmons. 
§ 21. As the result of my observations in these two regions of Pennsylvania, I stated 
in 1878, that the passage in the central valleys “from the Upper Cambrian shales into 
the Silurian sandstones is gradual, and that there is no stratigraphical break ; although, as 
shown by Rogers, such an interruption occurs between these same sandstonesand the 
underlying slates along the north-west border of the great Appalachian valley.” 
This non-conformity has been questioned by Prof. Lesley, but my own observations 
at the Lehigh Water-gap are confirmed by those published by Mr. I. C. White, in 1882, in 
his Report G. 6, of the second geological survey of Pennsylvania, (pp. 150, 151) and I 
repeat his statement that “the proof seems conclusive,” that the Silurian sandstone, 
IV, here rests unconformably upon the underlying slates. Of these, we have already 
spoken as entirely distinct from those fossiliferous shaly strata which underlie conform- 
ably the same sandstones in the valleys of central Pennsylvania. 

* Second Annual Report on the Geology of Pennsylvania, 1838, page 36. 
+ Chem. and Geol. Essays, 2nd ed., preface, p. xxi. 
Sec. 1V., 1883. 29. 
