NORMAL GEOTHERMAL GRADIENT 109 
of the wells from 445 to 400 feet. As it is hardly to be expected that 
reliable information can be obtained from wells of such shallow depths, 
no further consideration will be given these observations in this 
paper. 
From DeGolyer’s (6) observations in Tuxpam, Mexico, there 
results the following reciprocal gradients by using all of the observa- 
tions, inclusive, between the indicated depths. 
Feet Feet per °F. 
Llano Grande 100-2 , 683 B27 
Tanhuijo 1 ,060-3,558 32.0 
Tlacolula 75-4,026 42.6 
Tlacolula 75-4,080 40.3 
Roy O. Armstrong has kindly communicated to the writer the 
results of two tests in the oil fields of Canada. Averaging the observa- 
tions by the usual least-square method, from a depth of 250 to 1,500 
feet, inclusive, in a well located in Sec. 17, T.19, R. 2W, sth, Alberta, 
the resulting reciprocal gradient is 71.1 feet per degree Fahrenheit. 
From a wellin the southern part of the field in Turner Valley, Alberta, 
the value 44.8 feet was obtained from a range of depths of 250 to 
1,267 feet. 
In marked contrast with these high temperatures in the oil fields 
of Mexico and Canada, we have the very interesting record of low 
temperatures obtained by Ralph H. Cleland (7) in the mining dis- 
tricts of Northern Ontario. 
Feet Feet per °F. 
Dome Mine Porcupine Dist. 248-3 ,005 164.0 
Hollinger : 235-3, 892 223.4 
McIntyre as 181-3, 865 233-2 
Kirkland Lake ¢ Kirkland Lake 2,490-4,905 130.7 
deck Hughes 2 I, 110-4, 225 137-9 
ake Shore 391-3,575 167.1 
Wright-Hargreaves ‘ os 587-3 ,003 118.4 
Sylvanite 495-2 ,993 142.2 
Frood : Sudbury 400-3 , 100 155.2 
The preceding averages were obtained by making least-square 
adjustments of all the observations recorded in each mine. 
GENERAL CONSIDERATIONS 
If our records represented true rock temperatures, it would be 
possible to draw tangents to the depth-temperature curves at desired 
depths. With smooth curves like those shown in Figure 2, it would 
be easy to make these determinations, and the results thus obtained 
would necessarily possess a physical significance not possessed by 
the successive straight lines used in this paper. However, imperfec- 
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