212 vraiTE: relations between coal and petroleum 



oils in sands overlying others, in the same geologic formation, 

 carrying heavier oils, may^ in many cases at least, be due to 

 differences in the mother organic deposits. However, the effects 

 of filtration are not to be overlooked. 



(7) In regions where the progressive devolatilization of the 

 organic deposits in any formation has passed a certain point, 

 marked in most provinces by 65 to 70 per cent of fixed carbon 

 (pure coal basis) in the associated or overlying coals, commercial 

 oil pools are not present in that formation nor in any other for- 

 mations normally underlying it, though commercial gas pools 

 may occur in a border zone of higher carbonization. The ap- 

 proximate carbonization limits of the rocks containing or over- 

 lying oil pools may -be found to vary somewhat in different 

 provinces according to the characters of the original organic 

 debris, the circumstances attending its deposition and the 

 geologic structure. 



(8) Wherever the regional alteration of the carbonaceous resi- 

 dues passes the point marked by 65 per cent or perhaps 70 per 

 cent of fixed carbon in the (pure) coals, the hght distillates 

 appear, in general, to be gases at rock temperatures. Occluded 

 oils may, in some cases, have escaped volatilization. 



The observations and conclusions here offered suggest a wide 

 range of problems, both scientific and economic, that merit 

 thorough investigation with greater refinement of criteria as 

 well as of methods. A greater volume of detailed analytical 

 data concerning petroleums is needed for comparisons from the 

 geographic and stratigraphic standpoints. Detailed paleonto- 

 logical- investigations should be made of the detrital organic 

 deposits laid down under different conditions in marine and 

 fresh waters, and the decomposition products generated in the 

 biochemical process, as well as in the dynamo-chemical process, 

 should be chemically studied in detail. 



Some of the features of the regional alteration of coals and 

 petroleums that are here lightly touched upon will be more fully 

 •discussed in a more extended paper now in preparation for 

 publication by the U. S. Geological Survey. 



