280 The Origin and Relations of the Carhon Minei'als: 



asphalt represents a group of substances of which the physical 

 characters and chemical composition differ greatly in virtue of 

 their derivation, and also differ from changes which they are 

 constantly undergoing. Thus at the Pitch Lake in Trinidad, 

 the central portion is a tarry petroleum, near the sides a plastic 

 asphalt, and finally that which is of almost rock-like solidity. 

 Hence we see that the solid residues from petroleum are unstable 

 compounds like the coals and lignites, and in virtue of their 

 organic nature are constantly undergoing a sei'ies of changes of 

 which the final term is combustion or oxidaticm. From these 

 facts we might fairly infer that asphalts formed in geological 

 ages anterior to the present would exhibit characters resulting 

 from still further distillation ; tliat they would be harder and 

 drier, i. e., containing less volatile ingredients, and more fixed 

 carbon. Such is, in fact, the case; and these older asphalts are 

 represented by Grahamite, Albertite, etc., which I have desig- 

 nated as asphaltic coals. These are found in fissures and cavities 

 in rocks of various ages, which have been more or less disturbed, 

 and usually in regions where springs of petroleum now 'exist. 

 The Albertite fills fissures in Carboniferous rocks in Isew Bruns- 

 wick, on a line of disturbance and near oil-springs. Precisely 

 the same may be said of the Grahamite of West Virginia. It 

 fills a vertical fissure, which was cut through the sandstones and 

 shales of the Coal-measures; in the sandstones it remained ojien, 

 in the shales it has been closed by the yielding of the rock. The 

 Grahamite fills the open fissure in the sandstone and was plainly 

 introduced when in a liquid state. In the vicinity are oil 

 springs, and it is on an axis of disturbance. From near Tam])ico, 

 Mexico, I have received a hydrocarbon solid — essentially Gra- 

 hamite, — asphalt and petroleum. These are described as occur- 

 ing near together, and evidently represent phases of different 

 dates in the same substance. I have collected asphaltic coals, very 

 similar to Grahamite and Albertite in appearance and chemical 

 composition, in Colorado and Utah, where they occur with the 

 same associates as at Tampico. I have found at Canajoharie, 

 Xew York, in cavities in the lead-veins which cut theUtica shale, 

 a hydro-carbon solid which must have infiltrated into these 

 cavities as petroleum, but which, since the remote period, when 

 the fissures were formed, has been distilled until it is now 



