THE SOUTH, OR DAUPHIN, FORK.
This fork, or arm, of the Southern coal-field is a long, deep, narrow, and single basin, being a continuation of the First, or Pottsville, basin, parallel with the Sharp Mountain, which forms its southern margin. The peculiarities of this basin, as we noticed them in the Pottsville district and as illustrated in figure 74, pursue it to the end.
Figure 94 is from R. C. Taylor's Statistics of Coal, and represents a section from the Sharp Mountain on the left, to the fourth, or Red Moun tain on the right. Mr. Taylor was quite familiar with this portion of the coal-field. He spent much time, under the Dauphin & Susquehanna Coal Company, in its investigation. We differ very much from Taylor in our sections generally, simply because we have availed ourselves of late developments. He wrote at an early day, without the light we now have, and we can only express our surprise and admiration at his general cor rectness. In the present instance there is little to add, with the exception of late developments in tunnelling across the basin, in which the company have discovered several seams not laid down in section 94.
We find here no deviation from the general order of the seams, except that the lower beds are split: the Buck Mountain, or B, forms two, and the Mammoth forms two, or perhaps three. But, as before mentioned, there are more seams developed since the late Mr. Taylor formed the fore going section, and twelve seams are now proved, which will include the measures from A to G or H. But in all probability G is the highest workable seam, and is cut in the Yellow Spring, tunnel at its lowest or synclinal axis, where the seam stands like a V, and is cut through its base, which is 40 feet thick. We must, therefore, conclude that, if the measures hold their average thickness, the depth of the basin is between 700 and 800 feet below the level of this tunnel.
We have before noticed the change from anthracite to bituminous coal in those fields; but no definite point has been fixed where the change com mences. It has been often said that the anthracite coals depreciate in
hardness from the Lehigh westward; but, though we have paid more attention to this matter than any one else, it has not appeared perceptible to 'us. We find the white-ash coals of the Pottsville district as hard, dense, and firm as those of the Lehigh, and there is little perceptible change this side of Swatara. We do not find the tendency to change fully developed until we reach the forks of the basin, and in these it is marked and rapid, and the western half of the Dauphin Fork is a full semi-bitu minous; while the Short Mountain coals may be termed a semi-anthracite, or a grade between.
There is no comparison to be made between the eastern coals and the red-ash of the central portions of the field, because these seams do not exist at either its eastern or western end, and all the red-ash coals that may be found at these extremities belong to the lower red-ash beds,— generally A and B.
The red-ash seams produce much soft and crumbling coal, and the con sequence has been that all the coals of the central portions of the field have been pronounced depreciated in hardness; while, on the contrary, the white-ash coals of the Mammoth are as hard, dense, and solid at the base of the Mine Hill as the Locust Mountain.
As a matter of interest, we may speculate on the probable breadth originally of the Southern coal-field, or how much it has been contracted. If we calculate the depth of the basins, their present angles, and probable ancient undulations, we will find in nearly all cases a contraction of nearly, if not fully, one-half: therefore, where the Southern coal-field is now 5 miles wide, it was, in all probability, originally 10 miles wide. But this rule will not hold good in any but the First coal-field generally, and the Mahanoy portion of the Middle coal-field.