61 
covered up Carboniferous beds between Leek and Rocester 
much in the same way as Permian strata overlapped 
Carboniferous between Knaresborough and Bramham Park, 
Yorkshire. He had given his views to the public, and 
there was no further occasion to occupy the time of the 
Society, but he might state that, he was prepared to main- 
tain his position on the ground where the sections were 
exposed between Stockport and Macclesfield. 
Dr. Joule, F.R.S., exhibited his current meter, and with 
it, in connexion with a galvanometer, made an experiment to 
determine the horizontal intensity of the earth’s magnetism 
in absolute measure; the result gave 3'83 as the value of this 
element in the hall of the Society. The current employed 
was produced by a single cell of a Bunsen’s battery. 
MICROSCOPICAL AND NATURAL HISTORY SECTION. 
January 3rd, 1870. 
R. D. Darbishire, B.A., F.G.S., in the Chair. 
Dr. Wm. Roberts exhibited some specimens of urinary 
calculi, composed of cystine ; also some crystals of the same, 
obtained by evaporation in the open air of the ammoniacal 
solution. Six-sided plates of mother-of-pearl lustre were 
obtained in this way, which formed brilliant objects for the 
microscope. 
