The Origin and Relations of the Carhon Minerals. 273 



From these facts it is app:irent that the cai'bon series is 

 graded geologically, that is, by the lapse of time during which 

 ])laiit-ti.ssue has been sn))jected to this natural and spontaneous 

 distillation. But we have better evidence than this, of the deri- 

 vation of one from another of the groups of residual products 

 which have been enumerated. In many localities, the coals and 

 lignites of diiferent ages have been exjiosed to local influences — 

 such as the outbursts of tr;ip-rock, or the metamorphism of 

 mountain chains, — which have liastened the distillation, and out 

 of known earlier groups have produced the last. For example, 

 trap outbursts have converted Tertiary lignites in Alaska into 

 good bituminous coals ; on Queen Charlotte's Island, on Anthra- 

 cite Creek, in southwestern Colorado, and at the Placer Moun- 

 tains near Santa Fe, New Mexico, Cretacedns lignites into 

 anthracite ; those from Queen Chirlotte's Island and south- 

 western Colorado, are as bright, hard and valuable as any from 

 Pennsylvania. At a little distance from the focus of volcanic 

 action, the Cretaceous coals of southwestern Colorado have 

 been made bituminous and coking, while at the Placer Moun- 

 tains the same stratum may be seen in its anthracitic and 

 lignilic stages. 



A still better series, illustrating the derivation of one form of 

 carbon solids from another, is furnished by the coals of Ohio, 

 Pennsylvania and Ehode Island. These are of the same age ; 

 in Ohio, presenting the normal composition and physical char- 

 acters of bituminous coals, that is, of plant-tissue generally, and 

 uniformly descending the scale in the lapse of time from the 

 Carboniferous age to the present. In the mountains of Penn- 

 sylvania the same coal-beds, somewhat affected by the metamor- 

 phism which all the rocks of the Alleghanies have shared, have 

 reached the st;ige of semi-bituminous coals, where half the 

 volatile constituents have been driven off ; again, in the anthra- 

 cite basins of eastern Pennsylvania, the distillation further 

 effected has formed from these coals anthracite, containing only 

 from three to ten per cent, of volatile matter ; while in the 

 focus of metamorphic action, at Newport, Rhode Island, the 

 Carboniferous coals have been changed to grajyhitio anthracite, 

 that is, are half anthracite and half graphite. Here, traveling 

 from west to east, a progressive change is noted, similar to that 



