284 



GRAVITATIONAL METHODS 



[Chap. 7 



extensively to map ridges of granite, gneiss, and Cambro-Ordovician rocks. 

 Examples are the Amarillo granite ridge, the Nocona-Muenster-Bulcher 

 ridge, the Healdton fields, the Criner hills, the Kansas granite ridges, and 

 the ridges in Colorado and Nebraska. Some of these appear in the 

 gravity map of Fig. 7-516. Barton has reproduced the torsion balance 

 results for the Muenster-Bulcher ridge,^" which showed well in the gradient 

 picture. However, in the Fox area, the Fox and Graham uplifts were 



Fig. 7-116. Torsion balance anomalies on Hull-Gloucester fault, Canada (after 

 A. H. Miller). 1. Shale and limestone under 70' of drift (5 = 2.6); 2. Limestone 

 (5 = 2.7); 3. Chazy shale and sandstone (5 = 2.5); 4. Dolomite (5 = 2.8); 5. Potsdam 

 sandstone (5 = 2.5); 6. Precambrian (5 = 2.8). 



hardly noticeable. Only after considering the regional gradient due to 

 the adjacent Arbuckle Mountains could a better agreement between struc- 

 tural and torsion balance data be obtained. 



In oil exploration the torsion balance has been widely used for the loca- 

 tion of faults. Eotvos was again first to point out this possibility. The 

 amount of published data is no measure of the actual scope of work on 

 fault problems. In 1927 M. Matuyama investigated step faults in Meso- 

 zoic slate (density 2.5) covered by alluvial material (density 2.0) in the 

 Kokubu plain near the Sakurazima volcano in Japan. ^^^ Results obtained 



1" Ibid. 



162 M. Matuyama, Japan. J. Astron. and Geophys., 4(3), 1-18 (1927). 



