Page:Popular Science Monthly Volume 79.djvu/431

Rh The semibituminous grade of coal is found in the southwestern part of the field, the anthracite in the northeastern. Between these two areas the grade of coal is intermediate between semibituminous and anthracite. The distribution of the grades of coal corresponds somewhat closely to the complexity of structure in the different parts of the field. The structure becomes more and more complex from the southwest toward the northeast. The grade of the coal has been made better with an accompanying complexity of structure.

The semibituminous coal has been shown to possess good coking properties.

A striking feature of the coals, and one which is likely to be a serious handicap to their utilization, is their crushed and sheared condition. In many of the surface exposures and in the tunnels, drifts and open cuts where development has been carried on, the coal is soft and friable. Even where fairly firm and unbroken masses of coal are found, they can be readily crushed. It is difficult to find large lumps of coal free from fractures and slickensided surfaces. During mining, such coal can not escape being badly broken, and the difficulties of shipping will be great. In the case of the anthracite, the crushed and friable condition is likely to seriously impair its market value. With regard to the grades of coal of coking quality the soft character may not be so serious in that the coal can be converted into coke before shipping. It is scarcely probable, in a region where the crustal movements have been so widespread and intense, that the coals below the zone of surface disintegration will be free from the crushed and fractured conditions so prevalent at and near the surface.