709 
to be remarkable. In the southern portion of the State, they have 
produced anticlinal hills and synclinal valleys ; but in the northern, 
anticlinal valleys and synclinal hills ; while mid-way there is a de- 
bateable land, which sometimes presents one set of phznomena, 
sometimes the other. These different conditions, the author says, are 
assignable to the nature of the formations acted upon; thus, where 
the anticlinal lines constitute hills they consist of the hard quartzose 
conglomerate underlying the coal strata; but where they occur in 
valleys, they are always connected with the soft portions of the coal- 
measures or the softer red shales. ~ 
The whole of the carboniferous regions above referred to, con- 
tain bituminous coal; but the detached districts on the Atlantic 
side of the Alleghanies and eastward of the Susquehanna river pro- 
duce anthracite, and it was to them that Mr. Logan more particu- 
larly directed his attention. These detached fields consist of a num- 
ber of long, narrow, irregular troughs, separated by anticlinal axes 
of the quartzose conglomerate or subjacent red shale, and they are 
distinguished by the names of the southern, middle and northern 
anthracitic coal regions. 
The southern region extends from Mauch Chunk on the Lehigh 
river nearly to Petersburgh on the Susquehanna, a distance of 70 
miles, but its greatest breadth does not exceed six. It is traversed 
by five anticlinal axes parallel to one another and to that which 
bounds the trough, the steeper escarpment being on the north side ; 
and the angle increases with each successive ridge, so that at the 
southern the strata have been elevated beyond the perpendicular 
and turned over, exposing beds many thousand feet below the coal- 
measures. Pottsvilie and Mount Carbon are mentioned as points 
where these phenomena are well exhibited. On inspecting the 
coal-seams in this neighbourhood, Mr. Logan observed, associated 
with every one he examined, similar stigmaria beds to those which 
he had previously described in his paper on South Wales* ; and 
he was enabled by them to detect the inverted position of the strata. 
The undulations in this coal-field render an estimate of the number 
of seams difficult, and Mr. Logan thinks that the 70 or 80 reported 
by the miners to exist, ought to be reduced to one-fifth. Some of 
the seams are of great dimensions, particularly that at the Room- 
Run and Summit mines near Mauch Chunk. The thickness. of 
this deposit, with its associated partings of carbonaceous shale and 
an interposed stigmaria bed, is 50 feet, and it is estimated that the 
seam must yield from 40,000 to 50,000 tons per acre. At the 
Summit mines the coal is quarried to open day. Beneath the entire 
mass is a thick bed of underclay filled with Stigmariz, and the oc- 
currence of a similar bed 7 or § feet above the bottom of the coal, 
supports, Mr. Logan says, the opinion of Prof, Rogers and the mi- 
ners, that the deposit in its progress westward splits into more than 
one workable seam. 
The middle anthracitic coal region consists of an aggregate of 
narrow troughs, also separated by ten parallel anticlinal ridges or 
* Ante, p. 275. 
