32 J. J. STEVENSON CAKBONIFEROUS OF APPALACHIAN BASIN 



some of them contain much mineral charcoal. The persistence of these 

 filmy layers throughout thousands of square miles is not the least re- 

 markable feature of this bed. The "Bearing-in," known in some locali- 

 ties as the "Bands,"' is not persistent in West Virginia, where along the 

 eastern outcrop the bed is often only double, with a mere parting, there 

 being no deposit between the benches. The coal is not the same through- 

 out the bed, and each bench is apt to show its own type, distinguishing 

 it as sharply from the others as though the partings were many feet 

 thick. The coal differs in volatile, in ash, in coking qualities, and in 

 sulphur; that from one bench is "brick;" from another, prismatic; from 

 a third, hard, with more or less of semicannel. Like other beds, the 

 Pittsburg occasionally carries some cannel; but this is unusual, occur- 

 ring only on the border of the field. 



The proportion of volatile shows variation geographically, as was 

 indicated long ago by Professor H. D. Rogers. Along a line passing 

 westnorthwest from Maryland to Ohio, the ratios between volatile and 

 fixed carbon in the several basins are : 



Maryland 4.47 to 4.78 



Salisbury 3.18 to 3.38 



Connellsville 1.81 to 2.07 



Lisbon 1.38 to 1.83 



Washington county 1 . 03 to 1 . 79 



These ratios are taken from Mr A. S. McCreath's analyses. This de- 

 crease is most marked along the westnorthwest line, but there is in a 

 general way a decrease northwardly in several of the basins. The 

 volatile is high throughout Ohio. In West Virginia, as shown by 

 Professor Hite's analyses, the volatile increases, there being as much 

 in the continuation of the Connellsville as in the southern Lisbon of 

 Pennsylvania; still farther south, on the line of the Salisbury basin, 

 the ratio is 1.4, while in Mason County, on the central line of the trough 

 the ratio varies from 1.04 to 1.33. 



The Pittsburg coal bed has its greatest thicloiess at the southeast, 

 in the Potomac areas of Maryland and West Virginia, where the Main 

 coal is 12 to 14 feet. Along a westnorthwest line in Pennsylvania the 

 thickness decreases, becoming 8 to 10 feet in the Salisbury, 8 to 9 in the 

 Connellsville, 7 to 8 in the Lisbon, 6 to 7 in the Wa3Tiesburg, and 5 to 

 6 in basins farther west. It retains the latter thickness into Ohio, but 

 more frequently approaching the lower figure. On the western outcrop, 

 in Belmont and Guernsey counties of Ohio, the thickness falls to 4 feet, 

 and at last to 3 feet 6 inches, the several divisions of the bed being still 

 distinct. North from this line the bed grows thinner, slowly in the 



