The Mine Hill formation is parted near its western end by the Peaked Mountain, and divided into two miniature prongs or forks, in imitation of the western division of the main coal-field. Here the main basin forms two distinct synclinals, divided by the anticlinal of Pickett, or Peaked, Mountain.
We have, perhaps, diverted attention from the bounding mountain ranges of this field by stopping to notice the Mine Hill basin; but it will be remembered that the Locust Mountain forms the north boundary about 20 miles along the eastern end, and enters the Broad Mountain. This range or mountain-plateau, then, forms the north marginal line of the field for a distance of about 20 miles to a point near the Falls of Swatara. From or near this vicinity Thick Mountain forms the north boundary past Tremont and beyond the main forks of the field to some indefinite point, —perhaps Klinger's Gap,—and from thence to the western extremity it is known as Short Mountain. Thus the bounding mountain-range to the north is locally named and known by the primitive nomenclature, which applied the cognomens from local features, without regard to geology or topography. The "Mine Hill" would be an appropriate name for the entire range, since it would be nearly continuous and would really form a bounding line from east to west, leaving the Mine Hill basin outside and independent of the main field,—as it is, with the exception, perhaps, of an uncertain connection near Swatara; but even here it is doubtful whether the underlying veins connect.
A section of the field in the vicinity of Swatara will be found farther on, from data furnished by Col. D. P. Brown, who is practically familiar with that portion of the coal-field.
The south boundary of the north fork is known as Big Lick Mountain it unites at the point of division with the Fourth or Stony Mountain, which forms the north boundary of the south or Dauphin fork, and at the west ern extremity with the Short Mountain, which is the terminal knob of the north or Lykens Valley fork. The Big Lick Mountain, above noticed as the north boundary of the south fork, unites at the western extremity of the Dauphin prong with the Sharp, or, as it is locally called, the Third, Mountain.
All these bounding mountains, with the exception of the Broad Moun tain, are monoclinal ridges, with crests of massive conglomerate and outward bases of red shale. Those on the south have north dips, and those on the north south dips, forming an interior undulating basin from crest to crest of those marginal mountains. A glance at the map will show the blue
outlines of those conglomerate monoclinals surrounding the basin, with the plateau of the Broad Mountain stretching from the First to the Middle coal-field. With this exception, the blue border is set in a wide frame of red shale, which not only partially surrounds the first coal-field, but com pletely envelops both the First and Second, or Southern and Middle, coal fields. The dark tints of the coal lie in long, narrow strips in the centre of those borders of blue and red, and exist in nature as portrayed in the map.
The interior of the coal-field is peculiar. Its topography and botany, as well as its geology, differ widely from the surrounding border. The interior ridges, with the exception of the Mine is of the same formation and character as the surrounding mountains,—are undulating and diversified. They conform to the water-courses more than to the anticlinals of the coal measures, and, consequently, roll in all directions, as frequently at right angles with the mountain-ranges as parallel with them. The interior sides of the marginal mountains are generally lapped with the coal measures half-way to their summits; but above the coal is exposed the white and massive conglomerate.
The softer shales, slates, and sandstones of the red-ash coal measures— the upper series of Rogers—form a warm, dry, and friable soil, which produces and supports a vegetation peculiar to itself or to such formations generally in this latitude, and not only to this, but to all the anthracite and bituminous fields. We notice, however, that the soils in the vicinity of the white-ash veins are colder and more silicious, and produce quite a different vegetation ; while the upper or red-ash coal measures produce the chestnut-oak, chestnut, dogwood, laurustinus, and such dry, warm-soil trees and shrubs : the lower or white-ash coal measures and the con glomerates support the resinous pines, swamp-oaks, hemlock, bay-laurel, ferns, &c., or such vegetation as grows in flinty, silicious soils or cold, low grounds.
The red shales lying below the conglomerates also support a warm growth of vegetation, similar to that produced by the upper coal-measures; but neither produces nor supports, to any extent, the botanical productions of a rich or luxuriant soil. The walnut, poplar, hickory, cherry, locust, elm, &c. do not exist within the anthracite coal-fields or in their vicinity.