BASINS, OR SYNCLINAL TROUGHS.
Figure 61 illustrates in a general way the undulations of the Shamokin coal-field or region, but does not represent the full number of basins, of which there are not less than 14 or 15 narrow synclinal and parallel troughs, or small subordinate basins. There are three prominent anticlinals within the region : namely, the Mine or Green Ridge, counting from south to north, the " Red Ridge," and the "Coal Run Ridge." These anticlinals start out from the Big or Shamokin Mountain on the northeast, and run parallel through the region to the Mahanoy or Locust Mountain on the southwest, dying down at a few points through the centre of the region, but holding their course consistently nevertheless.
Within these three principal anticlinals are ten other smaller anticlinals, or saddles, of less vertical and horizontal dimensions. These anticlinals, or saddles and ridges, divide the region into a corresponding number of basins, or synclinals : of these there are four principal ones, bounded on the south by the Locust or Mahanoy Mountain, and on the north by the Big or Shamokin Mountain, and traversed by the anticlinal ridges before mentioned. These three principal basins are again divided by numerous
subordinate saddles into a corresponding number of subordinate basins, which exist as long, narrow, parallel troughs. This frequent form of basin or saddle—synclinal and anticlinal—brings the seams in constantly recurring waves or undulations to the surface, and presents their outcrops in oft-repeated lines of strike. The hills, or dividing ridges, being gene rally of considerable altitude, this form of undulation consequently pre sents a large amount of coal above water-level, and brings all the coal beds within a reasonable distance from the surface. We presume none of the workable seams are over a thousand feet vertical in any portion of the Shamokin region ; and the Mammoth is accessible _.generally with a mode rate depth of shafting, say from 200 to 500 feet. But slopes are, or will be, generally in use in this region ; though to the present time most of the mining is done above water-level by drifts and tunnels.