GEOLOGY: W. BOWIE 
175 
regions below the general level and the 18 mountain stations above the 
general level. The range for local and the other two methods is, in 
each case, only 0 . 007 dyne. 
We must conclude that the regional distribution out to 59 kilometers 
is as likely to be true as the local distribution of the compensation. 
There may be some distance beyond 59 kilometers and less than 167 
kilometers which would show a smaller range in the mean anomahes 
than any of the distributions considered above. It seems to be reason- 
able to expect that the distance in question is nearer 59 than 167 
kilometers. 
Tests made to show which is the most probable depth of compen- 
sation indicated that when the stations were taken as a single group 
the value is about 60 kilometers. But when the stations were arranged 
according to the topography the depth of 95 kilometers is the most 
probable depth. The depths of compensation, determined from de- 
flections of the vertical,^ are from the first investigation 113.7 kilo- 
meters and from the later one, 122 kilometers. When the deflection 
stations in mountain regions only were considered the depth is 97 kilo- 
meters. The mean of this and the depth from gravity stations is 96 
kilometers. It is believed this is the best value from all geodetic data. 
It is improbable that the compensation is distributed uniformly 
from sea level to the depth of compensation. It is not probable that 
what may be considered the normal distribution of densities of the 
material in the outer portions of the earth obtains under all places on 
the earth's surface. 
The present data are not sufficient to enable one to compute the 
actual distribution of densities under any given area, but there are rea- 
sons to believe that approximations to the actual distribution may 
be made. 
In a study of the relation between the gravity anomalies and the 
geological formations, as indicated by surface material, it developed 
that at stations on the pre-Cambrian areas gravity is nearly always in 
excess. It is known that the older rocks have greater densities than 
normal and as this material is close to the gravity stations there should 
result a greater intensity of gravity. The excess of gravity at a station 
may give some idea of the depth of this older rock. 
The stations on the Cenozoic formations have a tendency to a defi- 
ciency in gravity. This seems to be logical as the rocks in this forma- 
tion have densities less than normal. Here again the size of the defi- 
ciency may indicate the approximate depth of the Cenozoic formation. 
The Paleozoic stations tend to be negative and the Mesozoic stations 
