GEOLOGY AND INTERIOR FORMATION OF THE FIELD.
Included in the Carboniferous strata we find the Vespertine sandstone, the proto- or subcarboniferous, and the Umbral red shales, both overlying the Ponent, or old red sandstone of the English, and underlying the con glomerate.
The vertical section on the left side of the accompanying map of the anthracite coal-fields is designed to illustrate the formation in the vicinity of Pottsville, from the Vespertine to the top of the coal measures. It will be noticed that the Vespertine is colored in the sections as in the map, while the Umbral red shale is the same in each; the conglomerate blue, and the coal a black tint. Thus the map and sections illustrate at a glance the geology of the coal formations, and will convey a better impression than words, or any written description, of the character and general formation of our coal-basins and their subordinate strata.
We have given four geological sections on the map :—first, a vertical section of the anthracite formations near Pottsville ; second, a vertical section of the Western or bituminous formations, which may be accepted as a general type of the great Alleghany coal-field, but not the more western coal-fields. We will give a general section of the more western
fields in connection with the Great Central coal-field of Illinois and Indiana.
The third section on the map is a transverse section from the Lehigh Summit mines, in the eastern end of the Southern coal-field, across the Lehigh basins, to the lower or western end of the Wyoming or Northern coal-field. The fourth is a transverse section from Pottsville, across the middle of the Southern coal-field, the New Boston or Broad Mountain basins and the Mahanoy region of the Middle coal-field, to the vicinity of Shenandoah City. From thence the continuation of the section is from Locust Gap across the Shamokin region of the Middle coal-field to Shamokin. The principal undulations are only given in the latter region.
The scale and the colors of the different formations will be sufficient to explain them, without further description.