BITUMINOUS AND ANTHRACITIC. 471 



which have been given by my brother and myself in another com- 

 munication, seem to claim for it a place in the present general 

 account of our coal-measures. The gradation may be thus briefly 

 described. Crossing the Appalachian coal-fields, northwestward 

 from the great valley, to the middle of the main or western trough, 

 by any section between the northeastern termination of the for- 

 mation in Pennsylvania, and the latitude of Tennessee, we find, 

 as the result of multiplied chemical analyses, a progressive in- 

 crease in the proportion of the volatile matter, passing from a 

 nearly total deficiency of it, in the dryest anthracites, to an ample 

 abundance in the richest caking coals. The existence of this 

 singular law of transition was first ascertained by me in 1337, 

 in which year I made mention of it in some public lectures. It 

 was communicated to the Association of American Geologists, 

 at their first Annual Meeting, in the spring of 1840 ; but I did 

 not publish it in print until the following winter, when it was 

 briefly alluded to in my fifth Annual Report on Pennsylvania. 

 Evidence of the existence of such a gradation in the coals of west- 

 ern Virginia, wifl be found in the Annual Reports of the Geolo- 

 gical Survey of that State, for the yeai's 1839 and 1840. These 

 historical references are here introduced, because the determina- 

 tion of the general fact was the result of many laborious analyses 

 of our coals, made by my brother and myself, and because at- 

 tempts have been made by others, to establish a claim to the 

 discovery. The lists of analyses contained in the Reports of the 

 Surveys of Pennsylvania and Virginia, and similar data not 

 yet published, show the following as the general proportion 

 of the bituminous matter, in the dilferent belts of the formation, 

 as we cross the region from southeast to northwest. 



First. In the most southeasterly chain of basins, the coal is, 

 for the most part, a genuine anthracite, containing sometimes, 

 however, a small per centage of bitumen, and always a little 

 gaseous matter, chiefly hydi'ogen. The quantity of the volatile 

 matter varies according to geological locality, from about six to 

 twelve or fourteen per cent. This first belt of basins embraces 

 aU the anthracite coal-fields of Pennsylvania, the slightly bitumi- 

 nous ones of Broad Top on the Juniata, of Sleepy creek, of the 

 Litfle North mountain, of Catawba creek, Tom's creek, Strouble's 



