226 Geological Society. 



attached to the stems, and extending in all directions through the 

 clay ; and they observed, in a gallery lighted on purpose, that the 

 stems seen in situ were very nearly all parallel to the planes of stra- 

 tification, only one being in an oblique position. Every stratum 

 underlying a coal-seam examined by Mr. Lyell, presented the same 

 phenomena, except one, and in that case the bed was so sandy that 

 it could not be considered as a fire-clay. The thickness of these 

 Stigmaria deposits varied from one foot to six feet. The roof of the 

 Blossberg coal-seams consists usually of bituminous slates, but occa- 

 sionally of very micaceous grit, and it contains great varieties of 

 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 r 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 gradation from the most bituminous to 

 the most anthracitic coal may be found in crossing the chain from 

 north to south*. 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 



* Sep papers by Prof. H. D. Rogers, Dr. Sillhnaii,&c. 



