278 



Scientific Geology. 



into a dark colored or anthracitous slate, which runs nearly east and 

 west, and dips north about 45°. But in no place have they found 

 pure coal : nor has any bed, even of that which is impure, been dis- 

 covered more than eighteen inches thick. The specimens hitherto 

 obtained, (No. 401,) are much mixed with pyrites and slate. 



It struck me that boring perpendicularly is not the most judi- 

 cious method of searching for coal at this place. I take it to be quite 

 certain, that the coal always occurs in layers between the laminae of 

 slate, and never in veins ; such a thing as a genuine vein of coal 

 being, as I suppose, inconsistent with the known laws of chemistry. 

 Hence then, as the strata dip 45° at this place, if a trench be dug deep 

 enough to lay bare the basset edges, crossing them at right angles, 

 it must certainly reveal all the beds of coal which the rock contains. 

 And since the loose soil is not more than ten feet deep, this must 

 be certainly the most economical course. The discovery of beds of 

 coal in other places by boring, leads often, I believe, into error : for 

 generally the strata containing coal are horizontal ; and then boring 

 alone will bring the beds to light : but where they are highly in- 

 clined, it is working to great disadvantage to bore into them perpen- 

 dicularly. I have found several times that foreign miners, who are 

 ignorant of the principles of geology, have led our citizens astray 

 by assuring them that the coal or the ore they are in pursuit of, lies 

 deep ; merely because such was the case in the particular mine in 

 Europe with which they were acquainted. 



In all the cases mentioned above, the anthracite occurs in a slaty 

 rock, either gray or nearly black, which is associated with coarser 

 aggregates. Many geologists would denominate this slate shale : 

 but I should rather term it argillaceous slate, or graywacke slate ; 

 because I prefer the system of Macculloch, which regards no rocks 

 as shale, which lie as low in the series as graywacke.* (Nos. 358 

 and 395 to 399.) 



In no case have I found anthracite in any of those anomalous va- 

 rieties of the graywacke group, which I have described; such as the 

 breccias, amphibolic, quartose, and talcose rocks. These I regard as 

 the oldest varieties of this formation ; and the anthracite I suspect 

 occurs among the higher members of the series. I know of no rea- 

 son, however, why this mineral should not be found in the oldest 

 varieties. That the slate in which it is found in Rhode Island, is 



* Classification of Rocks, p. 455. Also System Geology. Vol. 2. p. 248. 



