BROAD MOUNTAIN BASINS, ETC. ETC.
have now briefly described and illustrated the prominent anthracite coal-fields and their principal basins; and though we have not attempted to trace their axes, since we believe it to be impracticable, we have given a concise and practical illustration of each important division and district as faithfully and correctly as present developments will admit of; and we hope our readers will find instruction and pleasure in the details.
We have not written merely for one class of readers, and have, therefore, avoided scientific and technical phrases where plain, common words would best express the meaning, so as to be understood by the general reader. We know it to be a difficult matter to explain to the unprofessional, and those not familiar with geology, the intricate and irregular formations of the anthracite coal measures, which are so much distorted and changed from their normal conditions, or the original -positions in which geology teaches us they must have been formed. But when such descriptions and explanations are clothed in professional terms, and when technical and scientific names are given to local phenomena, or arbitrary specialties and nomenclatures are made use of such accounts become unintelligible to the ordinary reader, and are only comprehensible to the professional man or the student.
The little coal-basin which we have now before us for examination is the most simple and plain and yet the most perfect of all the anthracite formations, and will justify a more than ordinary description. It illus trates, we think, the phenomena of the anthracite coal formations more fully than any other basin, and exists as nearly in its normal or original condition as any cotemporary basin of the anthracite group.
It does not properly belong to any of the grand divisions of the anthra cite fields, but is a distinct and separate basin, though it connects, in a manner, the First with the Middle coal-field by the high, undulating plateau of conglomerate, known as the Broad Mountain, which rises from beneath the Mine Hill basin, forms the Twin crests of the Broad Mountain, with the Broad Mountain basin between them, and then descends into the Mahanoy Valley beneath the coal measures of the Middle coal-field.
Owing to the nearly horizontal strata of the Broad Mountain, and perhaps its original elevation above the Schuylkill and Mahanoy Valleys, this portion of the anthracite formations has been raised by the forces which contracted and depressed the flanking or parallel valleys : consequently, its strata have not been crushed and distorted, as the measures of those low, weak, and yielding basins were. We find, therefore, much the same result in physical appearance and geological structure as in the detached Lehigh basins, which were evidently formations of a similar nature.
The tendency, however, to form the vertical by contraction from the south (though the forces might be exerted equally from the north) in the north-dipping strata is still evident, both on the Broad Mountain and the Lehigh plateaus.
There are a few rare cases where the effects of contraction are more evident in the south dips than the north; or on the north instead of the south sides of peculiar basins.
One of these is at Coalcastle, in the case of the famous "Jugular" basin or "overthrow," and another may be found in the Head Mountain basin, on the eastern terminus of the Middle coal-field, east of the Catawissa Railroad, where the south dip is nearly vertical, and the coal thick, crushed, and evidently disturbed. We do not remember another instance of this character ; though it is quite possible that such exist. It is, how ever, a general rule throughout the anthracite regions for the north dips to assume a steeper angle than the south-dipping strata; and, as stated above, nearly all the perpendicular and inverted strata are on the south side of the basins.
We may mention here a style of basin, roll, or undulation that has merely been alluded to as existing within the principal or prominent basins, but which we have not discussed. As a critical mention may throw some light on subjects which we propose to illustrate in connection with the New Boston or Broad Mountain basin, we may here appropriately notice them.