300 Status of the Theory of Isostasy. 



geodetic work and chief of the computing division of 

 the U. S. Coast and Geodetic Survey, of his report on 

 "The figure of the earth and isostasy from measure- 

 ments in the United States." This memoir dealt fully 

 with the deflections of the vertical. It was followed the 

 next year by a supplementary report. In 1912 Hayford 

 and Bowie published "The effect of topography and 

 isostatic compensation upon the intensity of gravity." 

 This work was based upon data independent of the 

 deflections, but confirmed, in a general way, the results 

 of the other investigation. It has been followed by two 

 further and independent publications by Bowie. The 

 geodetic data have been treated in a similar manner for 

 India and the Himalayas by Crosthwait, Burrard, Hay- 

 den, and Oldham. Hecker has made many determina- 

 tions of gravity at sea, but the accuracy of the shipboard 

 determinations does not compare with the results on 

 land. The subject of isostasy has been discussed in 

 many articles, and contributory data have been supplied 

 from other regions, but under the present topic it is not 

 intended to give a complete review of the literature of 

 the past decade, nor to touch on that which is simply of 

 geodetic value. Certain papers which have direct geo- 

 logic implications will alone be considered. 



Hayford concluded that the geodetic evidence indicated 

 the existence of a high degree of local isostatic com- 

 pensation. In giving an interpretation in terms of area 

 and elevation, he predicted that future investigations 

 would show that the horizontal extent that a topographic 

 feature may have without a corresponding density would 

 be between one square mile and one square degree. Else- 

 where he stated that the evidence indicated, though it did 

 not prove, that the assumption of local compensation 

 was nearer the truth than regional compensation to even 

 the small distance of 18-8 kilometers from the station. 

 The average vertical departure of the surface from the 

 elevations giving perfect isostasy he stated in 1909 and 

 1910 to be less than 250 feet. 



Thus Hayford was of the opinion that plateaus or 

 basins over 25 miles in diameter and more than 250 feet 

 above or below the mean level must be largely accounted 

 for by corresponding variations in density extending, if 

 uniformly distributed, to a depth of about 76 miles, the 

 perfection of relationship increasing with the mass of 



