176 
GEOLOGY: W. BOWIE 
positive, but there is no such evident relation between the densities 
and the gravity as with the two other formations. The average densi- 
ties of the Paleozoic and Mesozoic rocks are about equal. 
There is given below a table which shows that relations exist between 
the gravity anomalies and the geological formations in the United 
States. A positive anomaly indicates an excess in gravity and a nega- 
tive anomaly a deficiency. 
Relation Between the Gravity Anomalies and the Geologic Formation 
GEOLOGIC FORMATION 
NUMBER OF STATIONS 
MEAN ANOMALY 
With plus 
anomalies 
With minus 
anomalies 
All 
With regard 
to sign 
Without re- 
gard to sign 
Pre-Cambrian 
12 
2 
14 
+0.019 
0.023 
Paleozoic '. 
23 
49 
72 
-0.011 
0.021 
Mesozoic 
25 
11 
36 
+0.009 
0.017 
22 
32 
55 
-0.007 
0.019 
A study was made of the stations in India, 73 in all, and these showed 
that gravity at Cenozoic stations is, in general, too small. There were 
very few stations in the other formations which made it impossible to 
draw any definite conclusions from them. 
Relation Between the Gravity Anomalies and the Geologic Formation for 
Stations in India 
GEOLOGIC FORMATION 
NUMBER OF STATIONS 
MEAN ANOMALY 
With plus 
anomalies 
With minus 
anomalies 
All 
With regard 
to sign 
Without re- 
gard to sign 
Pre-Cambrian 
6 
2 
8 
+0.002 
0.025 
2 
3 
6* 
0.000 
0.009 
1 
0 
1 
+0.022 
0.022 
11 
20 
31 
-0.017 
0.028 
* One anomaly is zero. 
The larger part 'of most of the larger anomalies may de due to defi- 
ciencies or excesses in the densities of the materials below sea level near 
the stations, and these deviations from normal may be compensated 
in the lower strata. If this is true, isostasy is more nearly perfect than 
has generally been supposed. 
There are 42 stations in Canada which were studied but their gravity 
values showed no such relations to the geological formations as were 
found in the United States and in India. 
From the values of gravity at 358 stations in the United States, Can- 
