Anthracite. 



279 



closely allied to primary rocks, is obvious from the fact it abounds in 

 veins of asbestus — and the same mineral penetrates the anthracite. 



So full a description of the external characters of the Rhode Is- 

 land anthracite has been given by Prof. Silliman, in his Journal of 

 Science,* that it seems unnecessary to repeat it in this place. I shall 

 merely notice some peculiar characters, which, if I mistake not, have 

 an important bearing upon the theory of the origin of this mineral 

 and its connection with plumbago. In comparing this coal with the 

 anthracite from Pennsylvania, one is struck with the superior semi- 

 metallic or plumbaginous aspect of the former ; as I have already 

 remarked. But mere resemblance to plumbago is not all : for, says 

 Professor Silliman, " many of its surfaces are covered with a thin 

 film of a substance not to be distinguished from plumbago, as it has 

 the same lustre and softness, and stains the fingers and marks paper 

 in the same manner. A true plumbago is found occasionally among 

 the slates which accompany this anthracite." But in respect to the 

 Pennsylvania anthracites he says, "there is rarely on these surfaces 

 a plumbaginous aspect ; and when it exists, it is less remarkable than 

 in the Rhode Island coal." In the Worcester coal, I would also state, 

 that the metallic aspect is much more distinct, and the quantity of the 

 substance " not to be distinguished from plumbago," much greater. In- 

 deed, several tons of it have been ground and sold for plumbago. t 

 The anthracite found at Cumberland, Rhode Island, also, " is more 

 slaty than that of Portsmouth, it soils the fingers more, and approach- 

 es graphite." J The specimens from the recent exploration in Wren- 

 tham, bear a resemblance in appearance to the anthracite from Rhode 

 Island. 



Now do we not ascertain from the preceding facts, a gradual pas- 

 sage from anthracite to plumbago 1 And if my view of the relative 

 age of the Pennsylvania, Rhode Island and Worcester anthracites, as 

 they have been expressed in the first part of my report, are correct ; 

 we see that, this gradation corresponds to the relative antiquity of the 

 rock containing the mineral : that is, the older the rock, the nearer 

 does the mineral approach to plumbago. I may not indeed, have 

 shown, very conclusively that the graywacke formation of Massachu- 

 setts and Rhode Island is older than the anthracite formation of Penn- 



* Vol. 11. p. 87. 



f Robinson's Catalogue of Minerals, p. 78 

 t Cleavland's Mineralogy, vol. I. p. 501, 



