128 PECKHAM — THE GENESIS OF BITUMEXS. [April!, 



I have already shown (§ 6) that sediments become crystalline at 

 very low temperatures and that the crytalline schists below the low- 

 est stratified rocks contain abundant evidences of organic forms. 

 Are we to suppose that there was no intermediate zone in which 

 normal metamorphism died out and faded into unaltered sediments? 

 We ought to expect to find the pyroschists in their normal condi- 

 tion. We ought to expect to find the coal altered or unaltered, ac- 

 cording to its proximity to the heated area. We should not expect 

 to find the carbonized remains of organic foims in rocks containing 

 bitumen ; for we cannot suppose that those beds that yielded the 

 bitumen by distillation were suddenly plunged into a condition of 

 igneo-aqueous fusion by which the organic constituents were in- 

 stantly converted into anthracite and gas. As a general rule the 

 process of conversion must have been as gradual as the progress of 

 deposition. We cannot assume that in every instance the anthra- 

 cite is the residue from a distillation of which the distillate was 

 completely lost. Moreover, the example cited in § 7 is a com- 

 plete demonstration, occurring as it does in a region rich in bitumen, 

 that the change from sediments to crystalline schists is progressive 

 and involves the organic as well as mineral constituents of the 

 strata. 



17. If a traveler should leave Boston, Mass., and travel in a 

 generally southwest direction toward San Diego, in southern Cali- 

 fornia, he would encounter along his route a series of object les- 

 sons that would lead to but one conclusion. Whatever the age of 

 the crystalline rocks of New England may be, they are certainly for 

 the most part older than the Carboniferous. The small basin around 

 Mansfield, Mass., extending into Rhode Island, which contains the 

 anthracites of that region, is surrounded by crystalline rocks, and, 

 indeed, the anthracite beds themselves are, as already stated, al- 

 tered to a substance nearer graphite than coal. The coal slates 

 contain only impressions of coal plants, and fossils of any descrip- 

 tion are extremely rare in the vicinity. Intrusions of trap are fre- 

 quent, and cones of highly basic porphyrys are thrust up through 

 all of the crystalline sediments at several points. The change of 

 form has been very complete in respect to every constituent of the 

 sediments. 



Westward around New Haven, Conn., the bedding of the sedi- 

 icents has not been so completely obliterated, but the change in the 

 organic constituents has been quite as general. In the gneissoid 



