Intelligence and Miscellaneous Articles. 215 



estimated. The Whirlpool is on the site where the recession broke 

 down the partition separating the head of the Whirlpool-St. David's 

 buried gorge, and began to empty out the contents of this valley. 

 The cutting with the full power of the water of the four lakes varied 

 at times according to the height of the fall, and is calculated to 

 have occupied only 3500 years, for the cutting-back of about 4 miles 

 above the head of Foster's Flats. Thus the entire age of the Falls 

 is given as 39,000 years. 



May 1st. — Sir Archibald Geikie, D.C.L., Sc.D., Sec. U.S., 

 President, in the Chair. 

 The following communications were read : — 



1. ' On the Xerophytic Character of Coal-Plants, aud a Suggested 

 Origin of Coal-Beds.' By the Rev. Prof. George Henslow, M.A., 

 F.L.S., F.G.S. 



2. ' Penological Notes on the Igneous Bocks lying to the South- 

 East of Dartmoor.' By Harford John Lowe, F.G.S. 



The rocks described are contained in the Newton-Abbot district, 

 the region east of the Dart and south of the Teign. They are most 

 nearly related, both geologically and petrologically, to those of 

 South- West Devon, or the Plymouth district described by Worth. 

 The numerous intrusions occurring in the Devonian and Culm rocks 

 have been summarized by Dr. Teall as ' for the most part referred 

 to the basic kind known as diabases/ The Ashprington rocks are 

 finer-grained and lighter in colour than those of the other groups : 

 the Newton Devonian specimens range from light greyish-green to 

 nearly black, and in texture from fine to medium ; while the 

 Culm specimens are nearly all of coarser texture, occasionally 

 mottled, and on an average of slightly-darker shade. The masses 

 of igneous rock in the district do not display such evidence of 

 extreme dynamic stress as is found among the related rocks farther 

 west. The rocks described from the Devonian volcanic group 

 include tuffs, basalts, and diabases (mostly free from olivine, though 

 there are exceptions), picrite, leucophyre, and kersantite. The Culm 

 volcanic rocks show an absence of the finer-grained basaltic class, 

 as well as some distinct differences in mineralogical constitution 

 of the most nearly allied, indicating subjection to different physical 

 conditions. The rocks include tuffs, diabases, proterobases, epi- 

 diorites, camptonites, teschenites, hornblende-diabases, mica- 

 lamprophyre, and porphyry. 



XVI. Intelligence and Miscellaneous Articles. 



ELECTRICAL IONIC CONDUCTIVITIES. 

 BY PHILIP BLACKMAN. 



f\$ comparing the values given by the author (Phil. Mag. 1 ( J06, 

 ^ xii. p. 151) with those given by Kohlrausch (Leitvermogen 

 der Elektrolyte), it is found that the conductivities of (1) the 

 H and + ions are greater, and (2) the OH and — ions are smaller 

 than Kohlrausch's values. But, on comparing the conductivities 



