OBJECTIONS TO HYPOTHESIS OF MURCHISON AND OWEN. 57 



folded and distorted basins, but in the Middle fields. The hardest an- 

 thracite is not found in the southwesterly or most plicated portion of the 

 Southern field. There semi-anthracite, even semi-bituminous, occurs, 

 while the harder anthracite is obtained at the other end of the field, 

 where the condition is becoming more like that of the other anthracite 

 fields. 



Influence of Dikes insignificant. — It seems hardly necessary to refer to 

 the supposexl influence of dikes in causing the greater hardness of coal 

 at the northerly end of the southern basin. It is well known that such 

 influence can be exerted to but a little distance. The coal-fields near 

 Richmond, Virginia, have been intersected by dikes sufliciently to test 

 this matter ; but there are few coals richer in volatile conbustible than 

 those near Richmond. The dikes in northeastern Pennsylvania are ex- 

 tensive, but they could not be a factor in this matter. 



Columnar Structure not Evidence of loss of Volatile though Consolidation. — 

 Columnar structure gives no evidence in favor of the supposition that 

 the coal has been subjected to the loss of volatile after consolidation. 

 The Imboden coal of Wise county, Virginia, with about 37 per cent; the 

 Pocahontas coal of Virginia, with 21 per cent ; the Pittsburg coal on 

 Scotts run, in ^lonongalia county of A\^est Virginia, with nearly 40 per 

 cent, and the same coal near Uniontown, Pennsylvania, with 36 per cent 

 of volatile, all have this structure almost equally well marked. 



OBJECTIONS TO HYPOTHESIS OF MURCHISON AND OWEN. 



Murchison notes that the line of tlie anthracite coal in the field west 

 from tlie Donetz river, Russia, coincides with tliat of the crystalline axis 

 of the southern steppes, and suggests that the igneous rocks of that 

 axis in their subterranean prolongation may have converted the super- 

 ficial coal into anthracite wliile hardening the grits and sandstones and 

 shale; but there is need of proof that granitic and schistose rocks have 

 any metamorphosin^ij power. The change in those rocks must have been 

 complete that they might be available as hypogene rocks to support the 

 coal. Certainly the coal-fields of eastern Virginia occupying basins in 

 the metamorphic rocks show no change due to the influence of those 

 rocks. It is much more likely that the crystalline axis of the steppes 

 formed the shoreline of the region from which the coal marshes extended 

 into the basins. The change in type of rock and the disappearance of 

 the limestones in that direction go to show the proximity of a shoreline. 



I>r. Owen's explanation is of the same sort. No rocks of igneous or of 

 metamorphic origin are to be seen anywhere near the coal-field ; but 



