710 WILLIAM HERBERT HOBBS 



province (Hayford's northeastern and southeastern groups of 

 stations). This supplementary list prepared upon the basis of a 

 minimum of abnormality of 35" of arc, but without including the 

 additional Pacific slope stations, is given in Table II, following. 



The stations listed in this table have been plotted and appear in 

 the map of Fig. 2 with some indication of the measure of abnormality, 

 and upon the map of Fig. 3 are found the points of higher seismicity 

 as determined by De Montessus upon the basis of recorded data, 1 

 which, however, of necessity give undue prominence to localities 

 of early settlement or of later importance commercially. 



General conclusion as to law of distribution of anomaly of gravity. — ■ 

 Hayford's own observations thus confirm the evidence derived from 

 other regions that anomaly of deflection of the vertical and of 

 gravity show large local defect or excess, and that these local 

 anomalies are in some way connected with the distribution of seis- 

 micity and with zones of dislocation. 2 We believe therefore that 

 the late Professor de Lapparent was correct when in 1903 he stated 

 with much force before the French Academy: 



I believe, therefore, that for the present we may claim that the sea upon 

 the one hand, and the continents upon the other, enter into the variations of 

 gravity there only where a dislocation puts into contact two crustal compart- 

 ments, one of which is depressed and one of which remains stationary or is 

 fixed 



One may add that even in countries where the surface does not reveal the 

 dislocations, a means is found for diagnosing the deep and hidden faults. 

 Finally, the relation of seismic regions to rapid variations in the anomaly of 

 gravity shows that it would be eminently proper to carry out such studies in 

 order to make known those provinces of our globe which have most to reckon 

 with the danger from earthquakes [translation]^ 



May not the truth, as in so many other controverted ques- 

 tions, lie between the extreme viewpoints ? It is possible to assume 



1 Count F. de Montessus de Ballore, "Les Etats Unis seismiques," Archives des 

 Sciences Physiques et Naturelles de Geneve, 4th period, V (1898), 201-16. See also 

 William H. Hobbs, "On Some Principles of Seismic Geology," Gerlands Beitrage zur 

 Geophysik, VIII (1907), Appendix, pp. 289-92, PI. 2; also, Earthquakes (Appleton, 

 1907), pp. 112-16. 



2 While magnetic data are available for the territory of the United States (United 

 States Magnetic Tables and Magnetic Charts for 1905 [Washington, 1908]), their dis- 

 cussion by Bauer is still unpublished, and it would be premature to discuss them here. 



3 M. A. de Lapparent, op. cit., pp. S30-31. 



