Geology and Mineralogy. 393 



Using paper, aluminium, or air as the radiator, as the bulb was 

 turned round the axis of the primary beam studied, the intensity 

 of a secondary beam was found to reach a maximum when the 

 direction of the cathode stream was perpendicular to that of 

 propagation of the secondary beam, and a minimum when these 

 two were parallel, one electroscope recording a maximum rate of 

 deflection when the other recorded a minimum. Many experi- 

 ments were made which proved the evidence of partial polariza- 

 tion conclusive. 



When heavier metals, such as copper, tin, and lead, which emit 

 a secondary radiation differing considerably in character from 

 the primary producing it, were used as radiators, no variation in 

 intensity of secondary radiation was observed as the bulb was 

 rotated. This result was not found to be affected by a consider- 

 able variation in the penetrating power of the primary radiation. 



Experiments were made with several X-ray tubes. — Proc. Hoy. 

 JSoc.j lxxiv, 474. 



II. Geology and Mineralogy. 



1 . Plans for Obtaining Subterranean Temperatures. — The 

 recently issued Year Book, No. 3 of the Carnegie Institution of 

 Washington, contains a report by G. K. Gilbert of the progress 

 made in developing plans for an investigation of the subterranean 

 temperature-gradient by means of a deep boring in plutonic rock. 

 Mr. Gilbert discusses in detail the importance of such an investi- 

 gation and the conditions that should be satisfied in the solution 

 of the place for the boring. The conclusion is reached that an 

 altogether favorable locality for the work is to be found in the 

 Lithonia granite district in Georgia. In regard to this region in 

 its applicability to the object in view, the author says : 



" In its general topographic character the Lithonia district is a 

 plain. The stream valleys, for the most part open, are excavated 

 to depths of 50 to 150 feet. A few rounded bosses of granite 

 project from 50 to 150 feet above the plain. The granite is sur- 

 rounded and in part overlain by schists, which appear to have 

 originally constituted the walls and cover of the batholithic 

 chamber. The continuity of the granite mass from outcrop to 

 outcrop is inferred from the close lithologic similarity found at 

 all the outcrops. This similarity includes not only composition, 

 but a peculiar and unusual structure, the granite having an imper- 

 fect schistosity, the planes of which are everywhere contorted. 

 It is therefore called by the State Geological Survey contorted 

 granite- gneiss. The rock is massive. Only a few joints were 

 observed, and these appeared to be occupied by thin veins, and 

 thereby sealed, so as not to affect materially the continuity of the 

 rock. The partings utilized in quarrying are parallel to the sur- 

 face and are usually not natural, but created by blasting. They 

 indicate a tendency toward exfoliation, which is one of the char- 

 acters of massive granite. In recent studies in the Sierra Nevada 

 I have found the tendency to develop partings parallel to the 



