556 
ferns, as well as other plants, agreeing, generically at least, with 
those common in the British coal-measures. 
Mr. Lyell next examined the anthracitic coal-district at Pottsville, 
on the Schuylkill, in the southern part of the Alleghanies. ‘This 
district had been examined and described, as well as modelled, by 
Mr. R. C. Taylor, and the model had been inspected by Mr. Lyell 
previously to his visit. The whole of Pennsylvania has been mapped 
by Prof. H. D. Rogers, by direction of the State Legislature. Mr. 
Lyell refers to this survey, and he states that, by consulting Prof. 
Rogers’s map, it will be found that the Alleghanies, or more properly 
the Appalachians, which, viewed geologically, are 120 miles broad, 
consist of twelve or more great parallel ridges, or anticlinal and syn- 
clinal flexures, having a general north-north-east and south-south- 
west strike, but in Pennsylvania a nearly east and west strike prevails. 
The strata are most tilted on the southern border of the chain, where 
their position is often inverted, and the folds become less and less 
towards the central ridges and troughs, which again increase in 
breadth the more northward their position, till at last-the beds are 
almost horizontal. The oldest formations also are chiefly exposed 
in the most southern or disturbed regions, where syenite and other 
plutonic rocks are intruded into the lower part of the Silurian series. 
It has long been observed, that the anthracitic coal is confined to the 
southern or Atlantic side of this assemblage of small parallel chains, 
and that the bituminous occurs in the more inland or less disturbed 
region; the conclusion, therefore, Mr. Lyell states, seems inevitable, 
that the change in the condition of the coal was a concomitant of the 
folding and upheaval of the rocks. The conversion, moreover, is 
most complete where the beds have been most disturbed; and there 
are tracts in Pennsylvania and Virginia, near the centre of the chain, 
where the coal is in a semi-bituminous state. Chemical analysis, 
likewise, has shown that a eradation from the most bituminous to 
the most anthracitic coal may be found in crossing the chain from 
north tosouth*. The associated shales, &c., of the disturbed regions 
exhibit no alterations. 
It has also been supposed that the anthracite belonged to the trans- 
ition, and the bituminous coal to the secondary period; but this be- 
lief, Mr. Lyell says, has been gradually abandoned, as the knowledge 
of the geological position and the fossil plants of the coal-districts 
have become better known. Both the anthracitic and the bituminous 
coal overlie the old red sandstone, and contain the same ferns, Si- 
gillarie, Stigmariz, Asterophyllites, &c.; and they are as abundant 
and perfect in the anthracite as in the bituminous coal. 
At the first point where Mr. Lyell, accompanied by Prof. Rogers, 
examined the Pottsville coal-measures, the strata are nearly vertical, 
being cut off by a great fault from the less inclined beds which 
form the northern prolongation of the measures. They present 
thirteen beds of anthracite, the lowest of which alternate with 
* See papers by Prof. H. D. Rogers, Dr. Silliman, &c. 
