548 JOSEPH BARRELL 



The following qualitative conclusions may, however, be drawn from 

 an inspection of the residuals. 



Maximum deflections are found on each side of the axial hne 

 not more than 40 km. distant. The deflections continue large for 

 at least twice this distance but not for three times this distance. 

 The existence of large residuals so close to the axial line shows con- 

 clusively that the outstanding mass is within the zone of compensa- 

 tion and apparently within its outer half, but the maintenance of the 

 size of the deflections without much change for a considerably 

 greater distance shows also that it is not merely a surficial and 

 linear mass. It must have considerable extension in depth. In 

 these indications it agrees therefore with the more precise solution 

 of limiting depth given for the Texas-Kansas region. 



Indeterminate evidence from anomaly contours. — -The map of 

 anomaly contours shown in Fig. 5, Part II, and reduced from Bowie, 

 does not in general throw positive light on the depth of the masses 

 which produce the anomalies of gravity. The necessarily general- 

 ized and smoothed-out character of this map has been discussed 

 previously, especially in Part IV. A map based upon more numer- 

 ous observations would show higher values of maximum anomaly 

 and more of them. The centers of outstanding mass and the 

 anomaly gradients would become better defined, and the distances 

 from epicenter to half value of Fv would average smaller than 

 shown at present. However, notwithstanding the defects, thirty- 

 two measurements were made on this map of the distances from 

 fifteen pronounced maxima to the anomaly contour of half value, 

 and in directions not toward other adjacent maxima. This dis- 

 tance was chiefly controlled therefore by the single dominating 

 mass. The measurements gave an average distance of 120 km. 



If the outstanding masses which gave these anomalies were 

 assumed to have the form of spheres, this would give their centers 

 a depth of 160 km. and imply the existence of marked heterogeneity 

 extending below the zone of compensation as given by Solution H. 

 If the average form were assumed, however, to be that oblate mass 

 shown in Fig. 9C, this distance to the contour of half value would 

 correspond to a depth of 100 km. But such assumptions as to 

 form are hypothetical and justifiable only as a step in successive 



