Geological Society. 213 



(3) The hypothesis made by Prof. Thomson that the atoms 

 of every gas split off hydrogen atoms, would be,, if true, of the 

 greatest importance. I have, in my paper, drawn the atten- 

 tion to the fact, that one finds in different gases the value 



of — of the hydrogen atom. The hydrogen atom raises on 



m 



the glass of the tube a fluorescence different from other gases. 

 1 found that the extreme value of — = 10 4 is always given bv 



the observation of that fluorescence. 



But, on the other side, I could observe that by a very minute 

 purification of gases the fluorescence of hydrogen becomes 

 very feeble. 



That has been and still is the cause that I prefer to think, 

 until stronger arguments are brought forward, that the value 



- = 10 4 , when found in other gases, is due to small residues 



m J ° 



of hydrogen. That the charged atoms of different gases do 

 really exist in the Kanalstrahlen is also shown by the discovery 

 made by Prof. Stark of the Doppler effect of the spectral 

 lines. 



Wiirzburg, May 1907. 



XV. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from vol. xiii. p. 763.] 



April 17th, 1007.— Sir Archibald Geikie, D.C.L., Sc.D., Ser.R.S. , 

 President, in the Chair. 



^HE following communications were read : — 



1. 'The Toadstones of Derbyshire, their Pieid-Kelations and 

 Petrography; By Henrv Howe Arnold-Bemrose, J. P., M.A., 

 F.G.S. 



The district over which the Toadstones are seen may be divided 

 into three main areas of volcanic activity, between which there are 

 no exposures of igneous rock. 



1. The North- Western or Miller's-Dale Area. 

 II. The South-Eastern or Matlock Area. 

 III. The South-Western or Tissington Area. 



In each of these areas there are lava-flows, bedded tuffs, and 

 volcanic vents, and in the Miller's-Dale and Matlock areas several 

 intrusive sills. In the Miller's-Dale and Matlock areas the igneous 

 rocks are, with the exception of the Hopton vent, entirely in the 

 Mountain Limestone ; but in the third area they are mostly in the 



