Tlia, Origin and Relations of the Carbon Minerah. 270 



result of causes operating upon tliem after their production. 

 Near the surface, fhey are thicker and darker; below, and near 

 the carbonaceous mass fi'om wli ch they have been generated, 

 they are of lighter gravity and color. We find, in limited 

 quantity, oils which are nearly white, and may be used in lamps 

 without refining, — which have been I'efined, in fact, in nature's 

 laboratory. Others, that are reddish yellow by transmitted light, 

 sometimes green by reflected light, are called amber oils, these 

 also occur in small quantity, and as I am led to believe, have 

 acquired their characteristics by filtration through masses of 

 sandstone. Whatever the variety of petroleum may be, if ex- 

 posed for a long time to the air, it undergoes a spontaneous distilla- 

 tion, in which gases and vapors, existing or formed, escape, and 

 solid residues are left. The nature of these solids varies with 

 the petroleums from which they come, some producing asphal- 

 tnm, others paraffine, others ozokerite, and so on through a long 

 list of substances, which have received distinct names as mineral 

 species, though rarely if ever possessing a definite and invariable 

 composition. The change of ])etroleum to asphalt may be wit- 

 nessed at a great number of localities. In Canada, the black 

 asphaltic oil forms by its evaporation great sheets of hard or 

 tarry Msphalt, called gum-beds, around the oil-springs. In the 

 far West, are numerous springs of petroleum, which are known 

 to the hunters as ''far-springs," because of the accumulations 

 about them of the products of the evaporation and oxidation of 

 petroleum to tar or asphalt. Certain less common oils yield ozo- 

 kerite as a solid, and considerable accumulations of this are 

 known in Galicia and Utah. 



Natural paraffine is less abundant, and yet in places it occurs 

 in considerable quantity. Asphalt is the common name for the 

 solid i-esidue from the evaporation and oxidation of petroleum; 

 and large accumulations of this substance ai'e known in many 

 parts of the world, perhaps the most noted of all being that of 

 the "Pitch Lake" of the island of Trinidad; — there, as every 

 where else, the derivation of asphalt from petroleum is obvious 

 and traceable in all stages. The asphalts, then, have a common 

 history in this, that they are produced by the evaporation and 

 oxidation of petroleum. But it should also be said that they 

 share the diversity of character of petroleums, and the term 



