JuLY 19, 1923 BOWIE: ISOSTATIC INVESTIGATIONS 269 
were deep-seated or were the lack of isostatic balance of the earth’s 
crust near the groups of stations, there would not be such decided 
differences in the anomalies. 
The accumulated geodetic data seem to indicate very clearly that 
the causes of large gravity anomalies are very local and probably 
are masses of extra light or extra heavy material close to the gravity 
stations. This being the case, we must conclude that the earth’s 
crust is inamore nearly perfect state of equilibrium than has previously 
been supposed. 
Late in 1921, eight gravity stations were established on or near the 
Mississippi River Delta in order to test the isostatic equilibrium of the 
earth’s crust under the delta. A station already existed at New 
Orleans. 
The average anomaly with regard to sign at eight stations on the 
delta is —0.007 dyne. Four of the anomalies are negative and four 
positive. The results seem to indicate already that the crust under 
the delta is in isostatic equilibrium and that the delta material is not 
an extra load on the crust. The average negative anomaly is due to the 
presence of abnormally light materials near the gravity stations. This 
conclusion is opposed to that of Barrell. He believed a study of the 
deltas of the rivers Niger and Nile showed them to be extra loads.’ 
It is hoped that gravity stations may be established on other well 
defined deltas for there is no better geological formation on which to 
test the theory of isostasy. 
The really important problem in isostasy today is the use of the 
theory in geological research. The theory is widely accepted, but there 
still remains much confusion even in the minds of many of its advo- 
cates. Some claim too much for it while others do not give it sufficient 
credit. 
The geodetic data in the form of values of gravity and the deflec- 
tions of the vertical are facts. So also are the computed effects of 
topography. From these data we arrive at conclusions as to the isos- 
tatic condition of the earth’s crust. These conclusions cannot be 
classed as mere speculations for they are based on logical processes 
of reasoning. Of course, assumption must be made as to the distribu- 
tion of the isostatic compensation horizontally and vertically from 
topographic features. But even here there is evidence that the dis- 
tribution probably takes place within certain limiting distances. One 
of the results of the acceptance of the theory of isostasy will be the 
2 The strength of the earth’s crust, by Joseph Barrell, Journal of Geology, January- 
February, 1914. 
