THEORETICAL DISCUSSION. 
13 
traced from point to point by means of the drill, until the limits 
of the different beds are fairly well known. These sandstones are 
most numerous and attain their greatest thickness in the center of 
the region, only the upper beds extending to the western margin 
of the fields. In some localities two or more sands produce oil. 
Usually, however, the lowest sand is the most prolific. It often 
happens that gas is produced from a number of sands in one locality. 
The areas which have produced oil and gas have been of all sizes 
and shapes, and the depth of productive wells ranges from 100 to 
4,000 feet. It has been noticed, however, that in many cases the area 
of oil production is in the form of a belt extending for a number of 
miles and having but slight width compared to its length. The 
direction of these belts of productive territory is parallel to the 
principal geologic folds of the region. 
Drilling with the object of finding new productive territory is of a 
most speculative nature. Any one of five results may be the outcome 
of the well when the sand is pierced. (1) The sand rock may be 
found to be hard and close, incapable of holding oil or permitting 
the flow of any liquids through its mass; (2) the sand may be good 
but perfectly dry; or (3) it may be good sand and be completely 
saturated with salt water, which may fill the well to a depth of several 
hundred feet or even in some cases flow out upon the derrick floor. 
Favorable results may have any degree of success. (4) Gas may be 
found with hundreds of pounds of rock pressure to the square inch 
and in a volume of millions of feet a dav, or there may be only suffi- 
cient gas to serve a house or one or two boilers. (5) Oil may be 
encountered in such quantities and with such pressure that it will 
gush from the well at the rate of thousands of barrels a day, or there 
may be only a gradual seeping of oil into the well that will amount 
to but a barrel or two a day. 
THEORY OF ACCUMULATION OF OIL AND GAS. 
ORIGIN. 
The organic matter embedded in the shale which lies below and 
between the oil-bearing sandstones mentioned above may have been 
the original source of petroleum. This hypothesis is accepted in this 
paper, though such acceptance is not meant to imply that the hy¬ 
pothesis is established beyond question or that there are not facts 
and arguments which point to other sources of petroleum than the 
organic matter found in the accompanying sedimentary formations. 
Whether the petroleum comes from within or from below the 
shales, it must pass through them, and to do this it must pass through 
the very small pores existing in those relatively impervious beds. 
The nature and cause of this movement are not understood. Capil- 
