160 The American Naturalist. [February, 
surface as we proceed northward, until at the north end of the moun- 
tain we find the upper two members of the series only. 
“The structure of the mass may be summarized by stating that the 
beds have been thrown into corrugated folds which seem to have mod- 
erate, tolerably symmetrical corrugations at the south end of the moun- 
tain, but these corrugations deepen and become frequently overturned 
as we proceed northward. In the eastern portion of the area the axes 
of the reversed folds is generally westward. At the extreme south, 
the structure is a geo-anticlinal, but this develops in the central and 
northern parts of the area into a geo-synclinal owing to the continual 
disproportionate deepening and widening of one of its minor western 
corrugations. The general pitch of the beds is north. A less impor- 
tant southerly pitch which characterizes the northern portion of the 
area, in combination with the general synclinical structure in cross se 
tions, gives to all the mountain except its extreme southern portion 4 
basin-like character. The rocks are throughout strongly metamor 
phosed clastics, the orographic disturbances to which they, owe their 
marked crystalline character and porphyritic crystals having operated 
in several distinct periods. The Egremont Limestone shows à mark : 
diminution in thickness as we proceed southward in the area until it 
almost disappears. Throughout the mountain plain it is greatly modi- 
fied, being either a micaceous limestone or calcareous mica schist, oy 
graphitic schist. The graphitic rock is most developed near the schist 
contacts and in the southern portion is the only representative of the 
limestone (Journ: Geol., Vol. I, 1893). 
Origin of the Pennsylvania Anthracite.—In a recent Bullet 
of the Geological Society of America (Nov. 1893) Mr. J. J. Stevenson 
discusses the origin of the anthracite coal of Peensylvania. i 
stating the hypotheses that been advanced by Rogers, Owens, Murcht 
son and Lesley, to account for the variation in the volatile com’™ 
bles in Pennsylvania coals, and pointing out objections to each = ar 
the author offers one of his own, giving the facts upon which ge 
He conceives the coal-measures marsh to have had its origi? z 5 
east, and that it extended seaward after each period of accelerated 
sidence, so forming a new coal bed. One should find, accord 
hypothesis, a greater mass of coal in the northeastern portion 
Appalachian basin than in any other part, and also a greater haii 
ing to this 
‘on of the 
ie 
of conversion. Observation has shown that this is the case. and the 
also a direct relation between the increasing thickness of coal y Mr. 
decreasing volatile in Pennsylvania. This fact is demonstrated PY 
