MAHANOY REGION.
Figure 51 is a transverse section of the Mahanoy coal-basins, including the Broad Mountain or New Boston basin; which, however, does not properly belong to this region, and will not be considered in connection with the Middle coal-field, but rather with the Broad Mountain and Mine Hill basins of the first or Southern coal-field.
In this illustration, figure 51, a is the location of the New Boston basin on the Broad Mountain; b is the position of Mahanoy City, in the upper part of the Mahanoy Valley; c and d represent the locations, respectively, of Middle Mahanoy and North Mahanoy, or the second and third basins of the Mahanoy Valley. The Shenandoah basins are denoted by e, and the sharp, inverted anticlinals of the north dips: this, however, is also a trait of the formations at the south, in the vicinity of Mahanoy City. The view is presented looking west,--a being south, and e north. The Broad Mountain here bounds the coal-field on the south side, and the Locust Mountain on the north side.
Farther west, or down the valley, the Mahanoy Mountain starts out from the Broad Mountain and forms the south boundary of the coal-field; but at the western extremity of the Mahanoy region the Locust Mountain —crossing the coal-field from its north side—intersects the Mahanoy Mountain, and becomes from this point the southern instead of the northern boundary of the coal-field. The Shamokin Mountain forms its northern boundary from the vicinity of Centersville, or a point nearly opposite Ashland, where the Locust Mountain enters or commences to cross the coal-field. The Locust Mountain divides the field into its eastern and western divisions or regions. It is the northeastern boundary of the Mahanoy basins, and the southwestern boundary of the Shamokin basins.
The undulations of the Mahanoy formations are frequent and abrupt; the basins are deep, and the dip of the veins is frequently over 45°, and sometimes reversed, or both north and south dips are in the same direction, as illustrated in the vicinity of Shenandoah City. But these inverted dips also occur in other portions of the region, and, we believe, almost in variably on the south sides of the basins, as we find them in the Southern field, and particularly in the Pottsville district. Generally the south dips
are regular, but range from 30°, or less, up to GO°. From 30° to 45°, however, is about the mean of those south dips. There is an exception to these inverted north dips along the base of the Broad and Mahanoy Mountains, or on the southern extremities of the field. They occur locally in the interior of the field, or in the central basins, and are not general even in them.
A large amount of coal lies above water-level in the Mahanoy basins. The frequent undulations of the measures bring the veins to the surface in successive anticlinals ; and the hills or ridges within the coal-field being comparatively high and undulating in conformity with the coal measures, the coal is frequently exposed above water-level, and made available by the numerous water-courses crossing their strike and denuding the coal-strata. In this respect there is a great uniformity between the Mahanoy and Schuylkill basins ; and in the general form and dip of the veins and basins themselves there is a like conformity. A more general likeness exists in form and feature, both of surface and coal-formation, than even between the eastern and western portions of the Middle coal-field. The Mahanoy Valley or field is narrower than the Schuylkill, and the hills appear to be higher ; but we think the appearance is deceptive, and that there is really little difference except in the item of breadth.
In regard to the veins there is more difference. The lower veins in the Mahanoy are generally larger and more productive than they are in the Schuylkill region. The Mammoth vein and those immediately above it do not vary much from the same veins here, except in their uniformity and perhaps greater purity. But the veins below the Mammoth are greatly in excess of the same beds in the central portions of the Schuylkill region, and are more in conformity with the beds of the Lehigh basins.