166 
KIRTLEY F. MATHEK 
strongly suggests the possibility that at some such depth certain 
of the finer grained sediments may be nearly or quite devoid of 
moisture. If so, oil entering or present in the small pores of 
these shales would be broadly disseminated throughout the 
rock by capillary action. This is just the opposite movement 
to that requisite for the accumulation of oil in economic quanti- 
ties, but such migration may have been preliminary to certain 
processes of accumulation. 
The influence of such capillary migration upon the composi- 
tion of oils subjected to it is probably the only effect of quanti- 
tative importance to the oil industry. As suggested by Day, 
it is possible to explain the difference in the nature of the oil of 
different fields by the hypothesis ^That dark colored oil (possibly 
containing sulphur and asphalt) entered shales varying in frac- 
tionating-power, due to varying porosity or moisture,’’ and was 
there fractionated into oils of various colors and compositions. 
It is even possible, although in the opinion of the present writer 
scarcely probable, that the oils from the Carboniferous rocks 
of Pennsylvania and vicinity are ^The same as the Ordovician 
limestone oils of Ohio, with the sulphur removed by diffusion.” 
Furthermore, the long series of quantitative tests made by 
Gilpin and Cram^- indicate that the paraffin hydrocarbons dif- 
fused farther than the unsaturated or asphaltic hydrocarbons 
which were consequently left behind in migration due to capil- 
lary attraction. The strong contrast between the paraffin oils 
of Pennsylvania and the asphaltic oils of California may be an 
illustration of the effect of capillary dispersal resulting in frac- 
tionation or filtration . in the one case and the absence of this 
action in the other. 
Differential capillarity of oil and water; experimental data 
In the experiments conducted by Day, Gilpin and Cram, 
above referred to, in which crude oil was drawn upward by 
capillary action into tubes packed with dry fuller’s earth, the 
J. E. Gilpin and M. P. Cram, The fractionation of crude petroleum by 
capillary diffusion, U. S. Geol. Survey, Bull. 365, 1908. 
