1896. ] NEW YORK ACADEMY OF SCIENCES. 121 
mine and all points examined south from it the coal is anthra- 
cite; whereas at all points north from it to the border of the 
eruptive rock one finds only transition coal. 
Direct contact appears essential to change. The occurrence 
of anthracite in the 6th level south of the White Ash mine sug- 
gests that the upper plate comes down to the coal for a short dis- 
tance before changing its course into higher beds of the section, 
or possibly that a dike exists there like that in the upper part 
of Coal cafion. If direct contact be necessary there is no diffi- 
culty in explaining the decreasing extent of change observed in 
the coal as one follows it from the centre of eruption. 
The cause of the crushed or friable coal is not far to seek, the 
limits of that material being fairly well defined. It is found 
near the border of the upper plate, in the space where the influ- 
ence of the metamorphosing agent is becoming markedly less. 
Undoubtedly the intrusion of the trachyte plates, each not far 
from 200 feet thick, caused crushing of the coal at all points as 
far north as the edge of the upper plate, but the effect appears 
to be more and more marked as one passes northward from the 
Lueas mine; for the anthracite soon shows a foliated structure 
in spite of the change in composition. Further down where the 
thickness of the upper plate becomes less and the compressing 
power above consequently less, the slipping and crushing due to 
the intrusion of the lower plate would become more effective. 
But beyond the limits of that plate there was only the uplifting 
influence of the lower, and the coal is not crushed sufficiently to 
injure it for commerical purposes, though the effect of the cer- 
tainly somewhat abrupt displacement is distinct in the many 
slickensides shown in all parts of the White Ash mine. 
Prof. J. F. Kemp describes the eruptive rock as a trachyte 
closely allied to andesite ; so that its outflow was early, possi- 
bly at the time of the Laramide elevation, when great outpour- 
ings of andesite occurred in Colorado, Utah, Wyoming and 
Montana. It may be true also that these intrusions were prior 
to the folding of the beds, though the fact that the sheets follow 
closely planes between the strata is not necessarily decisive 
upon this point. The feature of especial interest is that the 
coal was completely formed when the disturbance took place, 
there being not only no evidence of pulpiness but every evidence 
that the coal was hard. It was crushed into minute fragments, 
slickensided like the Utica shales of Franklin county, Pa., or 
laminated like the Vespertine coals of southwestern Virginia. 
It seems, therefore, reasonably certain that the process of con- 
version was complete before this disturbance began; complete 
not only in the lower beds, but also in the White Ash, at nearly 
900 feet above the bottom of the Laramie. 
