There are five principal basins across the Mahanoy end of the Middle coal-field in a line from New Boston to Shenandoah City. Within these basins are several smaller undulations or rolls, as shown in the basin b, figure 51; but those rolls are local and have no great length of strike or axis; and the principal basins also change in a westward direction, and become merged in basins of greater depth and extent. The five synclinals of figure 51 decrease to three, four, or five miles down the valley, and the four anticlinal ridges decrease to one in the vicinity of Girardsville; but though the ridges which mark the anticlinals in the upper portion of the valley become depressed or die out, the axis of one preserved. In plain mining-phrase, there are five basins and four "saddles—besides small subordinate rolls— in the section given from New Boston to Shenandoah (not including the former); while at Girardsville there are only three basins and two "saddles," besides several minor undulations.
Figure 55 is intended as a type of the measures in the vicinity of Mahanoy City, or on the transverse line of figure 51. Owing to the recent development of this region, some confusion exists in relation to the veins. The Buck Mountain, whose natural position is B, appears as C in the column. We are under the impression, however, that the veins are right and we are wrong, as well as the mining engineers of that section. But at present it is impossible to place the lower veins where they belong. That there is some error here seems more probable than that there is a dis placement, since the veins assume their proper relation in the more developed portions of the region, as may be noticed in the Locustdale section, west of Ashland.* On the Preston Coal and Improvement Company property, below Girardsville, the Mahanoy and Shenandoah basins unite, forming three deep, comparatively wide, and uniform basins. The Locust Ridge and Bear Ridge anticlinals become depressed in this locality, and, instead of the conglomerate appearing on their axis, the lower veins pass over them and form a continuous bed from the Mahanoy to the Locust Mountain.
The Mammoth on this property is in good workable condition, about 25 feet thick. This vein is generally most productive and reliable when in its natural dimension, which varies from 20 to 35 feet. Any great increase or decrease above or below these sizes generally, though not inva riably, diminishes its value and productiveness. The Buck Mountain, Skidmore, or North Vein, as it is locally called, also exists in its best dimensions and most productive condition; while the Primrose and one or two overlying veins are favorably developed.
The coal-field here is nearly two miles wide, which is rather less than its breadth five miles farther east; but the amount of coal is nevertheless greater.
There is some confusion in the identity of the veins and the application of names in this section of the coal-field. But we have found so much general consistency in the relative positions of the main coal-veins, and so much uniformity in the veins themselves, that we do not hesitate to name them here, as elsewhere, in their general order. There are, however, exceptions taken to this order by some of our engineers, as represented in the columnar sections which we have given. C of our nomencla ture does not exist in their sections of this portion of the coal-field, unless it exists as the Big North Vein. In that case B, or the original Buck Mountain, has grown poor and lean at the expense of C, which has proportionally increased in bulk. We cannot accept this theory for fact, since we find the true relations restored in the neighboring basin of New Boston, where the Buck Mountain vein B exists in its proper position and natural condition. The altered position of this vein may be better under stood by a reference to figure 55 in the Mahanoy vertical section, where C is evidently the Buck Mountain vein, though occupying a position much above its proper location in the coal measures.
The accompanying sections of the several veins in the Preston tract will testify strongly as to their identity. The Mammoth, of course, there can be no mistaking : it is the superior bed of the anthracite fields, and so pre eminent that no other vein can approach in magnificence of size or pro duction.
The Buck Mountain, below the Mammoth, is the next in size and pro ductive character; while the Primrose is the most important seam above the Mammoth. Within this range of the coal measures there are seven workable veins, including the three named, all of which belong properly and generally to what are known as the white-ash coals; though the lower bench of the bed B is invariably red-ash, and sometimes of a deep-red color, as noticed in our description of the original Buck Mountain vein, page 194, Chapter IX .; while the Primrose is generally considered as a pink or gray ash. The Primrose bed, or G, is generally from 12 to 14 feet thick on this property, and is sometimes found pure, without slate or bone. It varies, however, from 10 to 20 feet in thickness, and frequently contains small part ings of bone.