THE STRENGTH OF THE EARTH'S CRUST 



539 



the mean depth of masses producing these deflections is probably 

 much less than 79 km. They belong, therefore, to the outer half of 

 the zone of compensation. 



TABLE XXVII 

 Distances between Adjacent Large Deflections of Opposite Sign 



There are other areas, however, as in the Adirondacks, Maine, 

 Michigan, and the Great Basin, where the distance between the 

 large deflections of opposite sign is considerably greater. So far 

 as this relation goes they could be due either to broad outstanding 

 masses in the zone of compensation or to much greater but more 

 concentrated masses in the nucleus beneath. But the general 

 relations to the magnitude and location of the gravity anomahes 

 as discussed later under that subject suggest that in so far as the 

 evidence is determinative these broader areas are also due to broad 

 excesses or deficiencies in the outer crust, not to masses in the 

 centrosphere. The data are not, however, in all areas of a suffici- 

 ently complete nature to give determinate solutions. In other 

 areas, however, detailed study following the lines of criteria previ- 

 ously developed can bring out very definite results in regard to the 

 location and depth of masses in spite of the interference of the 

 fields of force from various centers. An example of what may be 

 done by a detailed examination is shown under the next topic. 



Detailed study of the Texas-Kansas region. — -Fig. 12A shows the 

 deflections as given on a north-south fine of triangulation 1,000 km. 

 in length. The gravity anomalies are shown for distances of 200 

 km. on each side of the traverse. The stations are sufficient in 



