280 Scientific Geology. 



sylvania ; though the greater dip of the slate, as a general fact, in the 

 former, its more crystalline aspect, and the occurrence in it of crystal- 

 lized veins of asbestus and quartz, render this opinion probable. But 

 as to the anthracite formation in Worcester, it will be easy to prove, 

 in the proper place, that it is older than either of the others above 

 mentioned : and here it should be recollected we find the nearest ap- 

 proach to plumbago. 



The anthracite from these different localities exhibits, in its specific 

 gravity, a correspondent approach to plumbago. According to Dr. 

 Thomson,* the specific gravity of plumbago varies from 1.9 to 2.32: 

 but according to Beudant,f from 2.08 to 2.45. The first named au- 

 thor says, that he has never met with any anthracite whose specific 

 gravity was as great as 1.5 : Beudant, however, says it varies from 

 1.5 to 1.8. Now according to Mr. Bull, the mean specific gravity 

 of the Pennsylvania anthracite, from five localities; is 1.4364 He 

 states also the specific gravity of the Rhode Island coal to be, 1.438 : 

 But Prof. Silliman, who appears to have conducted the process with 

 great care, states the Pennsylvania anthracite to have the mean spe- 

 cific gravity 1.55, and that from the Rhode Island, 1.75.|| Mr. Bull 

 places the Worcester coal at 2.104. Upon the whole, though there 

 is not a little discrepancy in the above statements, we may, I think, 

 safely infer, that the Rhode Island coal is heavier than that from Penn- 

 sylvania ; and the Worcester coal the heaviest of all, and nearly equal 

 to plumbago. 



There is another fact that deserves to be noticed in this connection. 

 Plumbago, it is well known, contains so much iron, that some chem- 

 ists regard it as a carburet of iron. Now from the analysis of Mr. 

 Vanuxem, it appears that the Rhode Island anthracite contains a 

 much larger proportion of the oxides of iron and maganese, than that 

 from Pennsylvania ; even more than some specimens of plumbago. 

 Do we not in this circumstance perceive another evidence of an ap- 

 proach to that mineral in this ancthracite ? I am not aware that the 

 Worcester anthracite has been analysed ; nor have I time to attempt 

 its analysis before completing this Report. 



* Inorganic Chemistry vol. 1. p. 155. 



tTraite de Mineralogie vol. 2. p. 262. 



t Chemistry of the Arts. p. 33. 



II Journal of Science, vol. 11. p. 89 and 92. 



American Journal of Science, vol 10. p. 102. 



