1898.] PECKHAM — THE GENESIS OF BITUMENS. • 127 



sheets that form the table mountain of the Sierra Nevada were 

 poured out, not from a single peak, but from a whole range of 

 peaks ; when the whole of southern Colorado and northern New 

 Mexico and Arizona were covered with lava sheets thousands of 

 square miles in extent ; or when the valleys of West Virginia were 

 upheaved, the Oil Break formed and the mass of plastic grahamite 

 forced into the fracture ; or when the basic rocks that form the 

 mounds of iron porphyry in Cumberland and Foster, R. I., were 

 thrust up from the deeps ; and the trap dykes along the whole 

 eastern borders of the AUeghanies were poured into fractures of 

 local extent. But these convulsions that have brought basic por- 

 phyrys, basalts, trap dykes and local metamorphism to the surface, 

 have in the physical and chemical operations of nature produced 

 anthracites and anthracitic residues and not bitumens. Bitumens 

 are not the product of the violence of volcanic or cataclysmic action, 

 but of the gentler action of normal metamorphism exerted through 

 long periods, during which the volatile bitumen has been distilled 

 from sediments containing organic matter, and at the lowest possi- 

 ble temperature, without regard to time, as the sediments were 

 pressed down to an isothermal that admitted first of their distilla- 

 tion and then of the conversion of the carbon residues into graphite. 

 1 6. Dr. Hunt has left hundreds of pages in which he has shown 

 that the crystalline and eruptive rocks, as we know them, are altered 

 sediments. His argument is conclusive that the carbon that they 

 contain is derived from organic forms. When discussing bitumens 

 he shows, first, that the pyroschists do not, except in rare instances, 

 contain bitumen, and are not in the proper sense of the word bitu- 

 minous. Secondly, he shows that the pyroschists do not. ^' whether 

 exposed at the surface or brought up by boring from depths of many 

 hundred feet, present any evidence of having been submitted to the 

 temperature required for the generation of volatile hydrocarbons." 

 Thirdly, he shows that as the oil occurs in the limestone it could 

 not have been distilled. He further shows that the Utica slate that 

 is beneath the lower Devonian limestones is unaltered, and adds, 

 '' More than this, the Trenton limestone, which on Lake Huron and 

 elsewhere has yielded considerable quantities of petroleum, has no 

 pyroschists beneath it, but on Lake Huron rests on ancient crystal- 

 line rock with the intervention only of a sandstone devoid of organic 

 or carbonaceous matter.^ 



^T. S. Hunt, Essays, p. 169, ed. 1875. 



