474 ON THE PHYSICAL STRUCTUKE 



fact that we nowhere, not even in the most dislocated and dis- 

 turbed districts of the anthracite coal-field, find any traces of true 

 igneous rocks, that, by their contiguity to the coal, could have 

 caused the loss of its bitumen, is a circumstance in their geology, 

 which goes far to confirm the truth of the hypothesis. Precisely 

 in proportion as the flexm-es of the strata diminish in our progress 

 westward, does the quantity of the bitumen in the coal augment ; 

 but it is difficult to conceive how any such law of gradation could 

 have been the result of a temperature transmitted by conduction 

 from the general lava mass beneath the crust, for that would imply 

 a corresponding increasing gradation in the thickness of the crust, 

 advancing westward under the coal-fields, whereas such an infer- 

 ence is in direct conflict with the fact of the general diminution 

 westward of the Appalachian rocks, besides being inconsistent 

 with all correct geothermal considerations, which forbid our 

 imagining so unequal a conduction to the surface, of the earth's 

 interior temperature. 



On the Physical Structure of the Appalachian Chain, as 



EXEMPLIFYING THE LaWS WHICH HAVE REGULATED THE ElEVA- 

 TION of GREAT MOUNTAIN ChaINS, GENERALLY. By W. B. 



Rogers, Professor of Natural Philosophy in the University of 

 Virginia, and H. D. Rogers, Professor of Geology in the 

 University of Pennsylvania. 



Having, in the prosecution of the State Geological Surveys of 

 New Jersey, Pennsylvania, and Virginia, arrived at certain gen- 

 eral facts in the structure of the Appalachian chain, involving 

 some new considerations in Geological Dynamics, we propose, 

 in the present memon, to offer a description and theory of the 

 phenomena. As similar structural features would appear, upon 



