THE STRENGTH OF THE EARTH'S CRUST 



3" 



of loo feet of abnormal mass of density 2 . 67, is Hayford's figure. 

 As previously discussed it is thought to minimize too much the 

 thickness of equivalent rock. It is given, however, for compari- 

 son with the column derived from the use of 0.0024 as a divisor. 

 This is regarded as a better average figure, but for some cases at 

 least, as shown for Seattle, this also may give too low a result. 



TABLE XXIV 



It is seen that the excesses of mass indicated for Mauna Kea 

 and at Sorvaagen are each comparable in equivalent thickness and 

 extent to the maximum thickness of the Niger Delta if measured 

 by rock upon land, 5,450 feet. The departures from equilibrium 

 at Hachinohe, Japan, and Seattle, United States, are comparable 

 in thickness and area to the burden of the Nile Delta, the weight 

 in air of 3,600 to 4,200 ft. of rock. In weight as in area, therefore, 

 these deltas are seen to impose burdens on the crust no greater than 

 are found, by means of geodetic observations, to exist in certain 

 other regions where geologic evidence had not revealed them. 

 The accuracy of Hecker's method for determining the intensity of 

 gravity at sea has been called into question by Bauer^ so that, until 



' "On Gravity Determinations at Sea," Amer. Jour. Science (4), XXXI (191 1), 

 1-18. "Hecker's Remarks on Ocean Gravity," Amer. Jour. Science (4), XXXIII 

 (1912), 245, 248. 



