OUR PETROLEUM RESOURCES—PRATT 301 
over our country searching for petroleum, setting up hundreds of 
independent wildcatting enterprises, drilling thousands of explora- 
tory wells every year for a generation. Our geographic frontiers 
having been subdued, we have searched out a new frontier in the 
vertical dimension, beneath the surface of the earth. The conquest 
of this new frontier has brought us our abundance of petroleum and 
the high living standards that it sustains. 
Every nation has this same vertical frontier but no other nation has 
explored it as we have. Over much of the earth, where the natural 
obstacles are no more formidable than those we have surmounted, 
political and social barriers have prevented the effective development 
of petroleum resources. We, too, might have failed had we not en- 
joyed our traditional freedoms. Restrictions by the State on the 
right to drill exploratory. wells, State ownership of minerals, State 
monopoly of rights to explore—any of these restraints would have 
gravely handicapped the search for petroleum we have carried out 
in the United States. Even the presence of a landed gentry with 
unbroken ownership over large areas, in contrast to our widely 
divided ownership in small tracts, would have seriously retarded 
our efforts. Our methods could not have been employed successfully 
in any other than an atmosphere of democratic free enterprise. 
If the wells we drill into the earth are successful they usually en- 
counter petroleum in the pores and small voids of marine sedimentary 
rocks. The petroleum is derived, we believe, from the organic re- 
mains of former marine life. Sedimentary rocks are the muds, sands, 
and oozes that have accumulated on the floors of seas in past geologic 
ages. The hardening of these materials into rock has taken place 
slowly under the pressure of the load of later sediments deposited on 
top of them. 
The search for the petroleum resources of the earth, taking account 
of this theory of origin, should be directed to those regions where 
in the past marine sediments rich in organic matter have been laid 
down in great depth and volume. Marine life, the source of organic 
matter, abounds in surface waters near shore, and marine sediments 
also are deposited in greatest volume near shore, where the streams 
from the adjacent land drop their load of mud and sand. But for 
sediments to accumulate to a great depth it is necessary for the sea 
floor to subside as fast as the load of sediments is laid down upon it; 
otherwise the area fills up and becomes land, and sedimentation 
ceases. Hence the search for petroleum turns to the unstable belts of 
the earth’s crust where there is delicate, prompt response to any change 
in load. 
Also it is necessary for the organic matter that results from abun- 
dant marine life to be preserved until it sinks to the bottom and is 
