NORMAL GEOTHERMAL GRADIENT 95 
With the exception of the C-group and the J-group, the results 
for the range, 100-1,000 feet, are quite consistent. The means for 
the other three ranges of depth show irregularities that increase as 
the number of wells decreases. That is, these means show the effects 
of the areal distribution of the wells. The effect appears also in the 
range, 100~1,000 feet, but to a lesser degree on account of the greater 
number of wells. 
AVERAGES DEDUCED FROM TABLES II AND III 
Tables II and III have been constructed on the same general 
plan as Table I. The object of these tables is to take into account 
the variation of temperature with structure. Hence, in Table II, 
only those wells are considered that are highest on the structure. 
In Table III, the wells that are supposed to be lowest on the structure 
have been included. On account of irregularities in the observations, 
cases can be found in which the most rapid rate of temperature in- 
crease is not found on the crest of the structure; in fact, in a few 
instances, just the reverse of these conditions exists. In general, how- 
ever, variation of temperature across a structure is much more prob- 
able than no variation, and in the observed exceptions to the rule, 
it is highly probable that a variation exists, so that the assumption 
of a variation regardless of the positions of the wells is a closer ap- 
proximation to the facts than is the assumption that geothermal syn- 
clines stand in correlation with geological anticlines. Furthermore, 
exceptions in these cases are offset by numerous other cases, par- 
ticularly in Wyoming and the salt-dome area of the Gulf Coast, 
where the lowest recorded gradient is high on the structure. For ex- 
ample, the highest reciprocal gradient recorded at Lance Creek, 
Wyoming, is 42.7 feet per degree Fahrenheit. As this well is near the 
top of the structure, it is not unreasonable to assume that the re- 
ciprocal gradients in the area surrounding Lance Creek are equal to or 
greater than 60 or 70 feet per degree. Hence, it is believed that the 
averages here obtained are approximately correct representations of 
the actual conditions to be expected on anticlines and domes. 
The tables show that the mean depth of 63 wells on the crest of 
the structure is 2,316 feet; the same for 63 wells on the flank, is 2,489 
feet. This shows that a majority of the wells in which there is a rapid 
rate of temperature increase are located on or near the crests of the 
structures. 
Comparison of the last two columns of tabulations shows that 
Table III agrees with Table I in that minimum values of 1/6 are 
found in the last column. The predominating curve represented in 
755 
