18 C. E. VAN ORSTRAND 
kilometers or more is reached. As this is the level of isostatic adjust- 
ment, it follows that the evidence supports the Pratt hypothesis. One 
defect has entered into the calculations. It has been assumed that the 
temperature gradient is constant. This gives a temperature at the 
depth of isostatic equilibrium which is about twice that obtained by 
Adams and Jeffreys as recorded in Table I. To obviate this difficulty, 
it can be assumed that the depth to the level of isostatic adjustment 
is known, and then from the equations can be determined the dis- 
tribution of temperatures down to that depth which reduces the iso- 
therms to planes at the isostatic level. 
TABLE II 
RISE OF ISOGEOTHERMS BENEATH APEX OF MOUNTAIN 

East Portal West Portal 
Rise of Isogeo- Rise of Isogeo- 
Tangent Plone thermal Plane Tangent Plane thermal Surface 
Depth, Depth, 
Kilo- Temp., Meters Feet Kilo- Temp., Meters Feet 
meters 5Ce meters aCe 
° fe) 672.5 2,207 fo) ° 674.4 ALOU 
10 316 153-4 503 10 350 126.9 Al6 
20 632 88.2 290 20 701 71.5 235 
30 949 62.0 203 30 I, O51 49-9 164 
40 1,265 47.8 157 40 1,401 38.3 126 
50 1,581 38.9 128 50 1,752 31.1 102 
60 1,897 32.8 108 60 2,102 26.1 86 
70 2,213 28.4 93 7° 2,453 22.6 74 
80 2,530 25.0 82 80 2,803 19.8 65 
go 2,846 22.3 73 go 3,153 17-7 58 
100 3,162 20.2 66 100 3,504 16.0 52 
POROSITY AND TEMPERATURE 
Laboratory tests prove that moisture greatly increases the con- 
ductivity of soils (14). The same condition apparently holds for solid 
rocks (15). A comparison of the depth-temperature curve (16) with 
the porosity curve (17) of a deep well, Ransom No. 1, Syracuse, 
Hamilton County, Kansas (Fig. 3), shows that whereas the porosity 
decreases with the depth, the temperature gradient increases with 
the depth. That the latter variation may be dependent on the mois- 
ture in the rocks is readily shown by considering that the product of the 
thermal gradient and the thermal conductivity represents the con- 
stant flow of heat through a vertical column of unit area. As the depth- 
temperature curve shows that the gradients increase with the depth, 
it follows from the relation of constancy that the conductivity, like 
540 
