UNDERGROUNI) MIGRATION OF OIL AND GAS 
165 
Apparently ^^the size of the capillaries is of great consequence 
in these diffusion phenomena. Finely divided material, such 
as amorphous silica, has no observable fractionating-power 
on oils that are readily fractionated by dry clays. Quartz 
sands likewise exhibit practically no selective action, but dried 
shale of Devonian age proved to exert an action similar to that 
of fuller^s earth. 
As shown by Engler and others, there is no chemical change 
in this process; fractionation by capillary dissemination is 
merely a mechanical separation of slowly diffusing liquids from 
those which pass more rapidly into the capillary spaces. 
Application to the conditions existing in the earth 
Except in arid regions, the pores of all sedimentary rocks 
near the surface of the earth are more or less completely filled 
with water; but the deeper levels which have been penetrated 
by the drill in the Appalachian oil fields and elsewhere are ap- 
parently dry. Oil field waters will be discussed in a subsequent 
section of this paper; it is here only necessary to call attention 
to the fact that the amount of water found in the sedimentary 
rocks of most oil fields decreases with depth. In the Appa- 
lachian region ^ffresh water is found in appreciable amounts in 
one or more beds as a rule to a maximum depth of 200 to 800 
feet. Brackish or salt water occurs below the fresh water at 
depths ranging from 400 to about 3000 feet. In a few wells 
out of the thousands drilled, salt water was found at greater 
depths than 3000 feet, but in all cases the amount and head of 
this water was very small, regardless of the porosity of the 
containing bed. In many wells open porous sandstones from 
1000 to 3000 feet from the surface show no water. Many of 
these were found to take up, with surprising rapidity, water 
poured into the well in the process of drilling. This is by no 
means equivalent to stating that shales three or four thousand 
feet below the surface of the earth are known to be dry, but it 
“ M. J. Munn, The Anticlinal and hydraulic theories of oil and gas accumula- 
tions, Econ. GeoL, vol. 4, pp. 509-529, 1909. 
