Geological Society. 227 



coal overlie the old red sandstone, and contain the same ferns, Si- 

 gillariae, Stigmarise, 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 

 the uppermost strata of the coarse underlying conglomerate. The 

 southern wall of an excavation from which the coal had been re- 

 moved, and which wall occupied the place of the underclay, pre- 

 sented impressions of the stems and leaves of Stigmaria; and on 

 the more solid and slaty beds of the opposite wall, or original roof, 

 there were leaves of Pecopteris, reed-] ike impressions, and Calamites. 

 In the slightly inclined northern continuation of the coal-measures, 

 Mr. Lyell observed in the Peachmount vein, three miles north-east 

 of Pottsville, a bed of anthracite eight feet thick, overlaid by the 

 usual roof of grey grit, and underlaid by blue clay or shale with 

 Stigmariae. Impressions of ferns were likewise noticed in the coal 

 itself. Only one instance was met with in the Pottsville coal-district, 

 by Mr. Lyell and Prof. Rogers, of a Stigmaria, placed at right angles 

 to the plane of stratification. 



The Pottsville, or southern anthracitic coal-field of Pennsylvania 

 was illustrated by a section resulting from the former labours of 

 Prof. Rogers, under whose guidance Mr. Lyell examined the coun- 

 try. The following remarks may explain the general structure of 

 the country ; the names applied to the formations are not, however, 

 those previously employed by the American geologists, but those 

 suggested by Mr. Lyell, in conformity with the conclusions at which 

 he arrived after his tour in New York, and a comparison of the strata of 

 that state with their British equivalents. The contrast between the 

 relative importance of most of the Silurian and Devonian groups in 

 Pennsylvania and in New York, Mr. Lyell states, is very great, arising 

 from a larger portion of sandstones and grits in the Pennsylvanian 

 rocks. The section extends from north of Pottsville to the country 

 ranging immediately south of Orwigsburg. To the south of the 

 vertical coal-measures and the subjacent conglomerate there are 

 displayed successively — 1st, a vast series, composed of red shales 

 3000 feet thick, of grey sandstone 2400 feet thick, and of red sand- 

 stone 6000 feet thick, the whole being considered by Mr. Lyell as 

 portions of the old red sandstone ; and 2nd, of olive- coloured shale 

 containing Devonian fossils. The dip of the strata is either nearly 

 vertical or inverted. Still further south, and a short distance north 

 of Orwigsburg, the olive-coloured shales are succeeded by very highly 

 inclined or inverted beds of upper Silurian rocks flanking a protruded 

 band of lower Silurian strata ; and lastly, on the southern confines 

 of the section is a trough of the Devonian olive- coloured shales 

 resting on the upper Silurian strata. 



Beautiful exhibitions of the underclay with its associated plant, 

 and of the overlying roof with its distinct remains, were observed by 

 Mr. Lvell and Prof. Rogers at Tamaqua, in the southern coal-field. 



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