428 WILLIAM BOWIE 



coast stations is 0.021, practically the same as for the Hayford 

 method of reduction. This is, of course, due to the fact that there 

 is very little relief in the topography at the coast. The size of the 

 Bouguer anomaly for stations in the mountainous regions above 

 the general level is o . 1 1 1 dyne. The range is therefore o . 090 dyne. 



When we consider the mean anomaly with regard to sign for the 

 Bouguer method of reduction, we find a range for the groups from 

 +0.017 to —0.1 10 dyne. This is a total range for the groups of 

 0.127 dyne. If we should consider the individual stations, we 

 should find much wider ranges for the Bouguer values than for the 

 Hayford values. The total range for the Hayford values is from 

 +0 . 059 to — o . 093. The total range for the individual stations for 

 the Bouguer reduction is from +0.057 to —0.229. 



The values given above are conclusive proof that the condition 

 of isostasy exists to a rather remarkable degree, and that the theory 

 that the topography of the earth is not compensated for by a lack 

 of density under the continents and by an excess of density under 

 the oceans is far from the truth. 



The fact that the country as a whole is in a high state of isostatic 

 adjustment is evident from the values given above, but there are 

 local deviations from normal which may be due to a number of 

 causes. They may be due to departures from the state of perfect 

 isostasy, to an erroneous method of distributing the compensation 

 horizontally from the station, to an erroneous method of distribut- 

 ing the compensation vertically with respect to depth, to erroneous 

 values employed for the density of the topography, or to an 

 erroneous depth of compensation; or they may be due to the pres- 

 ence of material heavier or lighter than normal close to the station 

 but below sea-level. This extra or deficient density may or may 

 not be compensated for in lower portions of the lithosphere. 



There were made, during the investigation, certain tests which 

 throw some light upon the causes of the gravity anomalies. 



It has been held by some that the compensation of topography 

 is not distributed locally under the topographic feature, but is 

 extended horizontally to some unknown distance. It does seem 

 improbable that the compensation should be directly under the 

 topographic feature and not extended horizontally to a certain 



