(2.) On the Fluor-Spar of Aden.

Dr Fleming exhibited to the Society several beautiful examples of quartz and calcedony, in the form of cakes or circumscribed stalagmites, from the fort of Aden in the Red Sea, which had been sent to him by Dr Buist of Bombay. They were remarkable as having a few minute crystals of fluoride of calcium, the matter of which aggregated during the evaporation of the water, which had furnished, in greater quantity, the siliceous materials forming the support.