5 1 2 Geological Society. 



paratus placed in such a way that the light from the sky may 

 fall and be reflected from the base of the prism. 



The eye being directed along the upper edge of the short 

 or ten-inch bar, the latter is to be elevated or depressed just 

 until the faintest gleam of the substance is to be seen in the 

 bright light reflected from the prism's base, and which, if pro- 

 perly managed, will appear of a very pale blue or bluish- 

 green colour ; when this occurs the indicator will point out 

 the refractive power of the substance under examination. If 

 a very volatile substance, such as any of the aethers or hydro- 

 cyanic acid, should be the subject of experiment, I then am in 

 the habit of employing a small piece of flat glass of a dark co- 

 lour attached by means of the fluid, to be examined, with a 

 very slight pressure to the base of the prism ; this will effec- 

 tually prevent evaporation of the fluid for a period of suffi- 

 cient duration to enable any one with ease and precision to 

 determine the refractive index or power of such a substance ; 

 and in general I prefer using this for all liquids, as it permits 

 a more extended and uniform surface of the matter under 

 examination, and diminishes the liability to error. 



LXIV. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 472.] 

 June 29, 3. " IVf OTICE on the Discovery of Insects in the Weakien 

 1842. -L^ of the Vale of Aylesbury, Bucks, with some ad- 



ditional observations on the wider distribution of these and other 

 Fossils in the Vale of Wardour, Wiltshire." By the Rev. P. B. 

 Brodie, F.G.S. 



In a former notice (Phil. Mag. S. 3. vol. xv. p. 534) Mr. Brodie 

 announced the discovery of insects as well as a new genus of Isopods 

 in the Wealden beds of the Vale of Wardour, and in this communi- 

 cation he gives an account of additional localities in the same Vale, 

 where he has found both the insects and crustaceans, and of the strata 

 belonging to the Wealden series, in which he has obtained fossil in- 

 sects, in the Vale of Aylesbury. 



Vale of Wardour. — The precise spot noticed in the former paper is 

 a quarry at Dallards, and the first point to which the author now calls 

 attention, is situated about two miles to the south-east of it. The fol- 

 lowing section is given of the beds at the new locality, the dip being 

 slightly to the south : — 



ft. in. 



1. Top. Debris of rounded fragments of greensand and 



Portland stone, with their usual fossils, a few inches 

 thick. 



2. Chert, full of Cyclas ; it also contains occasionally 



Bufonites J 6 



