1868.] -.r^^ [IH'fivliaiii. 



one eqiuill}' unstable, j'et both derived from a source which has 

 varied but sliglitl}', if at all, through all geological epochs. 



The theory of M. Berthelot appears to me to derive less sup- 

 port from observed facts than any which has been proposed. It 

 was doubtless formed with reference to the petroleums of Penn- 

 s^'lvania, which are among the purest mineral hydrocarbons of 

 any found in large quantities. The very small proportion of 

 nitrogen existing in these oils, might perhaps be accounted for 

 as an accidental constituent of the limestone, or as being mechan- 

 ically mingled with the carbonic acid or watery vapor. Neither 

 supposition is at all probable, since free nitrogen possesses such 

 slight alhnities. It adds nothing to its support to admit that 

 the alkali metals do exist in the interior of the earth, in the free 

 state. The ver}^ great difference observed between the varieties 

 of petroleum, cannot be satisfactorily- explained upon any hypo- 

 thesis, that regards them as the results of the same process act- 

 ing upon like materials ; neither should it be expected that a 

 process yielding an almost " unlimited diversity" of products 

 under slightly varying circumstances, would furnish a uniform 

 result over a very wide area. Samples of Pennsylvania petro- 

 leum of the same densit^^, when gathered from Avidely separated 

 localities, furnish identical results upon anal^^sis ; so too do 

 California petroleums, though gathered from localities fifty 

 miles apart, and yet the two vai'ieties of oil are exceedingly 

 unlike. " It is moreover altogether erroneous, to attempt to 

 explain the causes of geological facts, by the aid of supposed 

 analogies with the complex apparatus of physical cabinets, 

 whose existence in nature could scarcely be conceived by the 

 boldest and most unrestrained imagination."* 



Too much has been assumed concerning the constitution of all 

 petroleums from the researches of the few investigators who 

 have studied Penns^dvania petroleum. Because Messrs. Warren 

 and Storer discovered that the same proximate principles exist 

 in that portion of Pennsylvania and Rangoon petroleums boil- 

 ing at or below 200° C, j'et not in the same relative proportion, 

 and not without admixture of different substances, it must not 

 be taken for granted that all petroleums contain those i^rinci- 

 ples. Very little is at present known concerning the more 

 dense portions of Pennsylvania petroleum having boiling points 



* Biscliot. Chem. and Phys. Geology, I. 2i'S. 



