petroleum possibilities or Florida 
53 
VOLCANIC PLUGS 
Volcanic plugs or intrusions coming up into sedimentary rock, in some 
instances, push up the strata in such a way as to form storage reservoirs 
for oil. 
Fig, 7 . Diagram illustrating conditions favorable to oil and gas accumulation 
by the intrusion of volcanic rock. 
'While some of the ways in which conditions may arise suitable for the 
storage of oil are thus accounted for, such enumeration of the structural 
conditions is necessarily incomplete. Any condition in the structure or 
arrangement of the strata within the earth that serves to trap and store 
oil and gas may afford production in commercial quantities. 
depth or oil wells 
A question often asked is the depth to which it is necessary to drill to 
obtain oil. This question probably is prompted by the supposition that 
oil can be obtained at any place, provided drilling is carried to a suffi¬ 
cient depth. Such, however, is not believed to be the case. In some lo¬ 
calities oil is obtained at a very shallow depth, while in other parts of 
the earth it is not reasonable to expect that oil can be obtained at any 
depth. At some localities oil has been obtained in commercial quantity 
at a depth of 100 feet or less. On the other hand, there are not a few 
