Geological Society. 695 



That the observed long-waved radiation is not emitted by 

 the quartz walls is $ therefore, an established fact, and it is 

 highly probable that it originates in the luminous mercury 

 vapour*. 



But the question is not solved, whether we are dealing with 

 a radiation of temperature or of luminosity. According to 

 measurements of Messrs. Kiich and Retschinsky f, the mercury 

 vapour of the quartz-mercury lamp possesses a temperature 

 which amounts to many thousand degrees. In this case, the 

 observation of such long- waved pure temperature radiation 

 is not impossible, if the radiating mercury vapour possesses 

 strongly defined selective absorption in that spectral region. 



The main result of this investigation is the fact that heat 

 rays of a wave-length of about 0'3 mm. may be extracted 

 from the radiation of the mercury-lamp in sufficient force 

 to permit an investigation of their qualities. The infra- 

 red spectrum thereby sustains another enlargement of 

 1J octaves. 



LXXXI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 3.9.2.] 



December 21st, 1910.— Prof. W. W. Watts, Sc.D., M.Sc, F.R.S., 

 President, in the Chair. 



rPHE following communication was read : — 



'The Keuper Marls around Charnwood Forest.' By Thomas 

 Owen Bosworth, B.A., B.Sc, F.G.S. 



The area under consideration comprises some 300 square miles, 

 including the towns of Leicester, Loughborough, Coalville, and 

 Hiuckley. As has been shown by Prof. Watts, the Charnian rocks 

 project through a mantle of Triassic deposits which once com- 

 pletely covered them. In numerous quarry-sections the relation 

 of the Keuper to the pre-Cambrian rocks is well exposed. 



The quarries generally have been opened in the summits of the 

 more or less completely buried hills. A quarry is so worked that 

 its outline follows the contour of the buried hill : consequently, the 

 section presents but a dwarfed impression of the irregularity of the 

 rock-surface. Nevertheless, considerable undulations are observed, 



* It is, moreover, not quite out of the range of possibility that this 

 long-waved radiation could consist of relatively very short Hertzian 

 waves, which are produced by electric oscillations in small mercury 

 drops. But it seems improbable that any condensation of mercury 

 vapour would take place in the path of the current, /'. e. in the hottest 

 part of the tube. 



t Kiich & Retschinsky, Ann.d. Vhys, xxii. p. 595 (1907). 



