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WILLIAM BOWIE 



one method of distribution of the compensation is more probable 

 than other methods. It is reasonably certain that any method of 

 distribution of compensation must have the effective depth of the 

 compensation at a distance of from 30 to 50 km. below sea-level. 

 By effective depth is meant such a distance below sea-level that the 

 effect of all the compensation condensed into a thin layer at that 

 depth would be the same as the attraction of the compensation 

 distributed from the surface to the depth of compensation. 



The absolute density of the material between the depth of 

 compensation and the surface of the earth is not considered by the 

 geodesist in making the corrections for the effect of compensation. 

 It is only deviations from normal density that he considers, and it 

 is not necessary even to know what the normal density is. 



It must be concluded that the cause of the gravity anomalies 

 is located below sea-level, and the evidence points to the probability 

 that at least a large part of the anomaly is due to extra heavy 

 and extra light material in the outer portions of the lithosphere 

 which is below sea-level. 



There have been found decided relations between the sign of the 

 gravity anomalies and the geological formation. This is evidently 

 due to the abnormally heavy and abnormally light materials in the 

 pre-Cambrian and Cenozoic formations, respectively. There were 

 found relations between the Paleozoic and Mesozoic formations and 

 the sign of the gravity anomalies, but it is not evident what has 

 caused this relationship. 



There is practically no relation between the character of the 

 topography and the sign and size of the gravity anomaly by the 

 isostatic method of reduction. This is a very strong argument in 

 favor of isostasy because all other methods of making gravity reduc- 

 tions which do not consider isostatic compensation show most 

 decided relations between the size and sign of the anomaly and the 

 character of the topography. 



The use of gravity stations in other countries with those in the 

 United States gave a gravity formula whose constants were prac- 

 tically the same as the constants of the gravity formula derived in 

 191 2 from data at 124 stations in the United States alone. In the 



