4 The American Geologist. July, ih96 
gradation in clioniical (•f)ni])usiti()n from top to bottom of the 
seam, debituminizatio;i having gone on longest and been 
strongest in the lowest layers. Hut published analyses do not 
reveal any such change that nuiy be regartled as of any value 
in this connection.* 
2. ('omj)osifc .sfrafijied character of Peunsjilrania aulhra- 
clte seams. Stevenson seems to have based his theory on the 
assumption that the thickest and typical beds of anthracite 
were practically solid coal from tloor to roof. Actual obser- 
vations and measured detailed vertical sections in the mines 
and strippings reveal the fact that these typical coal beds are 
in reality split up horizontally into numerous alternate strata 
of coal and shale, coal and tire clay, or coal and sandstone or 
conglomerate, as the case may be,f so that each seam as a 
whole is really a parallel series of lesser seams, precisely sim- 
ilar in stratigraphical and structural character to the coal 
benches and their "dividing slates" of the "Pittsburg" bed in 
the bituminous region. The split-up character of anthracite 
beds in Pennsylvania could therefore hardly furnish Dr. Ste- 
venson with the argument he uses in regard to the supposed 
longer exposure of accumulated coal material prior to burial 
beneath sand and mud. And a good reason is furnished for 
accounting for the practically uniform chemical composition 
of the various superimposed, 3^et separated, layers of coal in 
a seam, by the phenomena of the interstratitied beds of shale, 
etc., just alluded to. 
8. DebUuiiiinizatiou of coaJ a stage in iiietamorphosls. As 
any stage in debituminization of a coal bed is to some extent 
metamorphism, the stage we designate anthracite is a stage in 
the metamorphic process. Graphite is probably metamor- 
phosed anthracite, just as anthracite is metamorphosed bitu- 
minous coal, or bituminous coal is metamorphosed lignite. 
Mineralogists have not found it possible to establish any defi- 
nite line or stage where metamorphism in rocks begins or yet 
ends in the direction of liquidity — molten rock. In like man- 
ner the fossil and mineralized vegetable matter of coals (no 
matter of what kinds of plants it is composed) presents no 
*Cf. A. Ashburner: "Classification and Coiiiposition of Pennsylvania 
Anthracites," p. 1!», 1886. 
tCf. 2d Geol. Survi'v Pa., vols. AC, A2, etc. 
