290 



GRAVITATIONAL METHODS 



[Chap. 7 



nepheline basalt in Triassic Keuper marls. The vertical intensity anomaly 

 is shown for comparison. In 1926 and 1927 the torsion balance was used 

 in the investigation of magnetite deposits of Krivoj-Rog in southern 

 Russia in connection with magnetic surveys. ^*^ Two cases are known 

 where the torsion balance has been applied indirectly in the mapping of 

 lignite deposits. The deposit shown in Fig. 7-122 occurs in Tertiary 

 beds (density 2.1) and is bounded on one side by Triassic sandstone 

 (density 2.35). Hence, it was possible to outline it by locating the edge 



10 TTTWrprWTTTTTTrw^TTtT-^T 7rr 



w^^/ ' y ' ,^^^/'^^^^^^|^^^^^| » w^ '> ^ 



600 ^"^ 50o 



Fig. 7-123. Torsion balance survey of Caldwell pyrite deposit (after Miller). 

 Solid curve, observed; dotted, calculated anomaly. 



of the sandstone block. Edge and Laby have published a survey of 

 similar character. In the Gelliondale field in southeast Victoria the 

 lignite bed occurs in horizontal stratification in sandy beds about 100 

 feet from the surface. Since it is terminated by the sloping surface of 



"8 P. Nikiforov and others, Inst. Pract. Geophys. Bull., 4, 299-307, 315-330 (1928). 

 i«»H. Seblatnigg, Braunkohle, No. 23 (1929). 

 '" Edge and Laby, Principles and Practice, etc. (Cambridge Univ. Press, 1931) 



