white: kelations between coal and petroleum 211 



that the composition of the mother organic deposit largely regu- 

 lates the types of oils. It may account for the nitrogen, sulphur 

 content, color, etc., just as the nature of the ingredient debris 

 controls the types of the coals. On the other hand, we may 

 conclude that, further in parallelism with the residual coal 

 debris, the rank of the oils within each type is mainly governed 

 by the stage in the progressive alteration (really the natural 

 distillation) of the organic deposits. 



(3) In general, it is seen that the lowest rank oils of each 

 type are found in the regions and formations in which the car- 

 bonaceous deposits are least altered; that the oils in formations 

 showing greater alteration of the organic debris, as in sub- 

 bituminous coals, are of higher rank, the oils being still more 

 clearly of high rank in the regions and formations of bituminous 

 coals; and that in regions of still further alteration the oils are 

 still better, the highest rank oils being, on the whole, found in 

 regions where the carbonaceous deposits in the same or in over- 

 lying formations have been brought to corresponding higher ranks. 



(4) The effect of progressive regional dynamic alteration is 

 marked by a concentration of hydrogen in the distillates and a 

 concentration of carbon in the residual debris (coal, carbonaceous 

 shale, etc), 



(5) Abnormally light oils, occurring sporadically in pools of 

 lower rank are, in most cases at least, probably due to filtration, 

 though it is not improbable that, in some cases, these oils are 

 migrates from underlying formations of more advanced alteration. 



(6) In general, at a given point the oils found in successive 

 underlying formations or in stratigraphically lower sands in the 

 same formation are progressively higher in rank. In other words 

 the principle that the increase in the gravity of the oil is inverse 

 to the stratigraphic depth of the well, proposed by Engler, finds 

 its parallel in the downward increase in the carbonization of 

 coals, according to the law of Hilt.^i Occurrences of lighter 



21 Oils found so near the outcrop or at such shallow depths as to have per- 

 mitted the evaporation of the lighter hydrocarbons or the intrusion of oxygen 

 in meteoric water should be regarded with suspicion. 



