326 ■ Geological Society : — 



sound could invariably be heard as far against a light wind as with 

 it, and in some cases much further. On one occasion, when the 

 temperature at 1 foot above the grass was 38° and at 8 feet 47°, and 

 the speed of the wind was 1 foot per second at 5 feet above the 

 grass, the bell was heard 440 yards against the wind and only 270 

 with it. 



Since, therefore, on the nights of the experiments at Villejuif 

 and Montlhery it is stated that the sky was clear, that there was 

 dew, and the temperature recorded at the two stations shows the 

 diminution to have been downwards, it is argued that the effect 

 of the wind to render the sound less audible at Villejuif was com- 

 pletely balanced by the downward refraction of temperature. 



Another phenomenon recorded by Arago is, that while the re- 

 ports of the guns at Montlhery as heard at that station were 

 attended with prolonged echoes, this was not the case with those 

 at Villejuif. It is thought that this difference is sufficiently ac- 

 counted for by the fact that while Montlhery is surrounded by high 

 hills with precipitous or wooded sides, which must produce echoes, 

 the country in front of Villejuif is very flat and has not a tree 

 upon it for miles. 



In concluding the paper reference is made to the Appendix to 

 the last Report of the American Lighthouse Board, in which Dr. 

 Henry, the Chairman, gives an account of his experiments, extend- 

 ing over thirty years, and the conclusions to which they have led 

 him, both of which are in favour of the apparent stoppage of 

 the sound being due to refraction. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 170.] 

 Jan. 19, 187G. — John Evans, Esq., E.R.S., President, in the Chair. 

 The following communications were read : — 



1. "On some Unicellular Algae parasitic within Silurian and 

 Tertiary Corals, with a notice of their presence in Cdlceola sanda- 

 lina and other fossils." By Professor P. Martin Duncan, F.R.S., 

 V.P.G.S., &c. 



2. " How Anglesey became an Island." By Prof. A. C. Ramsay, 

 LL.D., F.R.S., V.P.G.S. 



The author described, and illustrated by sections drawn to scale, 

 the contours of the island of Anglesey and the adjacent parts of 

 Carnarvonshire, and noticed that the whole island may be regarded 

 as a gritty undulating plain, the higher parts of which attain an 

 average elevation of from 200 to 300 feet above the sea-level. 

 Similar conditions are presented by the country for some miles on 

 the other side of the straits ; and in both the general trend of the 

 valleys is north-east and south-Avest. The rock surfaces, when bare, 

 show glacial striae running generally in a direction 30° to 40° west 

 of south. 



The author indicated that the great upheavals of the crust of the 

 earth forming mountains took place long before the commencement 

 of the Glacial epoch, and that ordinary agents of denudation had 



