GEOGRAPHIC DISTRIBUTION OF PETROLEUM 
61 
While the importance of the temperature check on the activi- 
ties of denitrifying bacteria has been indicated, it is obvious that 
there must be a check of another sort as well. In any region 
where the bacteria are sufficiently active to denitrify the organic 
base of petroleum more or less completely, the fats would also be 
destroyed were such a check, not operative. 
It has been assumed by some writers that the formation of 
petroleum would in itself constitute an automatic check on bac- 
terial destruction by virtue of antiseptic products. This is not 
in keeping with the observed processes of decay, however, and 
it assumes, furthermore, that petroleum is formed almost, if not 
quite, as rapidly as the nitrogenous bases are destroyed. As a 
matter of fact, all evidence points to an opposite condition, the 
extreme slowness with which petroleum is formed. It is, 
perhaps, not far from correct to assume that the hydrocarbon 
substance in oil shales is the somewhat altered organic base 
which, after the lapse of an extremely great length of time, has 
not yet been transformed into the ultimate product, petroleum. 
It is only by hastening the process through destructive distil- 
lation that petroleum may be derived from these shales. 
There is, apparently, a check of a mechanical nature found in 
the accumulation of inorganic sediments. It is generally recog- 
nized that accumulations of soil and fine sediment materially 
limit the activities of bacteria. It follows that the more rapid 
the deposition of fine sediments, the more complete the check. 
In much probability the fineness of the sediments has been one 
of the most important of the factors determining the rock asso- 
ciations of petroleum. At any rate, petroleum is associated 
primarily with shales. The presence of nitrogen in varying pro- 
portions in petroleum would seem to testify to the effectiveness 
of the shales as a check on the destruction of organic matter on 
occasion. In the cases of marked proportions of nitrogen we 
may suppose, perhaps, that not only have the fatty portions of 
the original base been protected, but that not even all of the 
nitrogenous parts have been destroyed by bacterial activities. 
It may be assumed that in general the rate of sedimentation 
is slower in the equatorial belt than elsewhere, a fact evidenced 
