as have been
found in the tops of anticlines in water-saturated rocks, and farther
down the flanks of folds or in synclines in unsaturated rocks.

The localization of oil pools is evidently determined partly by original
organic deposition, often in alignment with old shore lines, and partly
by the structural, textural, and other conditions which trap the oil in
its migration from the source.

=Effect of differential pressures and folding on oil genesis and
migration.= Another organic hypothesis proposed somewhat recently[23] is
that oil is formed by differential movement or shearing in bituminous
shales, which are often in close relationship with the producing sand of
an oil field, and that the movement of oil to the adjacent sands is
accomplished by capillary pressure of water and not by ordinary free
circulation of water under gravity. The capillary forces have been shown
to be strong enough to hold the oil in the larger pores against the
influence of gravity and circulation. The accumulation of the oil into
commercial pools is supposed to take place in local areas where the
oil-soaked shale, due to jointing or faulting, is in direct contact with
the water of the reservoir rock. This suggests lack of wide migration.
This hypothesis is based on experimental work with bituminous shales.
The general association of oil pools with anticlinal areas is explained
on the assumption that anticlines on the whole are areas of maximum
differential movement, resulting in oil distillation, and that they are
ordinarily accompanied by tension joints or faults, affording the
conditions for oil migration. Data are insufficient, however, to
indicate the extent to which the anticlinal areas are really areas of
maximum shearing. As regards the exact nature of the process, it is not
clear to what extent differential movement may involve increase in
temperature which may be the controlling factor in distillation,--although
in McCoy's experiment oil was formed when no appreciable amount of heat
was generated.

The development of petroleum by pressure alone acting on unaltered
shale, as shown by these experiments, has been taken by White[24] to
have a significant bearing on the geochemical processes of oil
formation. Under differential stresses acting on fine-grained
carbonaceous strata under sufficient load, there is considerable
molecular rearrangement, as well as actual movement of the rock
grains,--thus promoting the distillation of oil