BULLETIN OF THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS 
VOL. 19, NO. 1 (JANUARY, 1935), PP. 78-115, 2 FIGS. 
NORMAL GEOTHERMAL GRADIENT IN 
UNITED STATES! 

C. E. VAN ORSTRAND? 
Washington, D.C. 
ABSTRACT 
The objects in preparing this paper have been, first, to prepare a brief summary 
of the gradients deduced from recent geothermal surveys in the United States; and 
second, to discuss the data thus summarized from the standpoint of a normal geother- 
mal gradient. 
INTRODUCTION 
In 1920, N. H. Darton (1)’ published a summary of geothermal data 
in the United States. With but few exceptions, the data for the 
individual states consisted of temperatures recorded in flowing wells. 
Since the appearance of Darton’s publication, the United States 
Geological Survey and the American Petroleum Institute (2) have 
added to the list the records of about 700 non-flowing wells located 
chiefly in the oil-producing states. These observations, including 
Darton’s records, have never been discussed from the standpoint of 
a normal geothermal gradient; but, in view of the constant use of the 
term in geological literature, it is necessary that the term be properly 
defined and that the limitations of the definition be determined, as 
nearly as possible, from existing data. 
HORIZONTAL AND VERTICAL VARIATION OF GRADIENTS 
Recent geothermal surveys have shown without question that 
geothermal gradients vary uniformly in both the horizontal and the 
vertical. Any attempt, therefore, to approximate to a normal gradient 
must take these two important variations into account. 
Variation in the horizontal is illustrated by reference to Figure 1, 
which represents the cross section of a typical oil field anticline. Ob- 
servations show that in a majority of cases the isogeotherms (a’’a’a, 
1 Published with the permission of the director, United States Geological Survey. 
? Geophysicist, United States Geological Survey. Manuscript received, June 28, 
1934. To the writer’s assistant, H. Cecil Spicer, special credit is due for very valuable 
and efficient service rendered in carrying out the extensive calculations involved in the 
preparation of this and other recent papers on geothermal gradients. 
* This and the following references are in the bibliography at the end of this article. 
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