TAMAQUA DISTRICT.
The narrow, contracted, and vertical character of the eastern formations of the basin is fully illustrated at Tamaqua, where the folded and tilted condition of the measures exhibits all the phenomena of depression and contraction. But here the coal is less injured in quality and quantity than at Nesquehoning, and, though more abrupt and at higher angles than at the Summit, the veins are, nevertheless, equal in character and production, if not in size.
The sizes of the beds, as illustrated in figure 69, are out of proportion; that is, they are too large in comparison with the same veins in other sections; but if drawn to a proper or corresponding scale with the extent of the basins, they would not be discernible. We do not pretend to project them on a corresponding scale, but simply give them to illustrate the formation, number of basins, saddles, (axis) dips, and the general con formation of the measures. In figure 69 we have the Sharp Mountain on the right hand and the Locust Mountain on the left of the view. The position of Tamaqua is near the centre, but more to the right than the left.
There are two main axes within the basin, and two subordinate rolls or folds: one of these is shown at the foot of the Sharp Mountain, to the east; the other is not represented, but lies within the west basin.
The eastern side of the basin has been more thoroughly developed than the west by shafting, and the folding of the strata, as illustrated, is demon strated by tunnels. The two centre basins have not been penetrated, nor do we know that the third basin, or the western synclinal, has been reached; but the coals on each side of the main basin have been pretty thoroughly developed by both drift and slope.
Figure 70 represents one of those sudden rolls, or folding of the strata, so frequently met with in the Southern coal-field. The one before us does not appear to have materially affected the accompanying seams; but it is evident that this simple fold of a single vein increases the apparent number of veins in the basin by two,—or produces two more in the original Tamaqua section than really exist. The seams appear in the face of the
hill as three distinct beds, but development has proved them to be synonymous. The sketch illustrates the character of this fold simply, and is not designed as an exposition of the accompanying strata. The en graving would seem to represent the enveloping strata as slate, but such is not the intention, since rock, or sandstones and slates, alternate invariably in the vicinity of the Mammoth, and this is supposed to be that vein.
We would call attention to the angle of the north dip on the face of the Sharp Mountain at this point. It will be noticed that, though high, it is not beyond a moderate working angle, or from 60° to 70°. And here the coal is good, and the veins generally workable; but farther west the angles of the north dips increase, until in the vicinity of Pottsville they are inverted, and the marketable value of the coal destroyed. This seems to be a general rule: the coal is seldom good on the vertical angles, and never, or very rarely, when inverted.
We may here notice, also, the increasing number of the anticlinals within the main basin.
At Nesquehoning we find but one principal anticlinal; at the Summit we find two within the main basin in Panther Creek Valley,—independent, however, of the undulation in the Summit basin; but, as this is a local formation of small extent, it does not properly affect the prominent anti clinals. We have, however, represented but one in our section across the basin at the Summit. The second anticlinal does not appear prominently until we reach a point farther west, and between Tamaqua and the Summit.
At Tamaqua we find two principal anticlinals and two subordinate ones; while in the vicinity of Pottsville we have five prin cipal anticlinals and several subordinate rolls or "saddles." There is always one basin or synclinal in each part of the main basin more than the number of the anticlinals, as may be noticed in any of the sections given, since the marginal mountains always form one basin, independent of the anticlinals which may divide them.