Royal Society. 383 



distinct and even. Hardness, 3*5 on the more facile cleavages 

 and their combination edges; 5*5 on the ends of the prismatic 

 concretions. Density, 2'77." 



Prof. Chapman also pointed out to me the existence of inter- 

 mingled carbonate of lime in the specimens which I had previ- 

 ously analysed, and showed that the loss by ignition was in part 

 carbonic acid. I have since found that the finely pulverized 

 mineral yields up nearly the whole of its lime with effervescence 

 to cold dilute hydrochloric acid, which does not attack the sili- 

 cate. This still retains its rose colour, and is a hydrous silicate 

 of alumina and potash with a little magnesia. The following are 

 the results of the analyses by myself of two specimens, purified 

 by dilute acid (one being from the same mass as the one given 

 above), and a partial analysis of a third specimen by Prof. H. 

 Croft, which he has kindly communicated to me. 





99-97 99-13 



The mineral freed from carbonate of lime seems to be constant 

 in composition ; and from its crystallization and density, as well 

 from its chemical constitution, to pertain to the felspars. 



Montreal, March 22, 1855. 



LV. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 309.] 

 January 18, 1855. — Sir Benjamin Brodie, Bart., in the Chair. 

 r r^HE following communications were read : — 

 -"■ " On the Dots upon the Valves of the Diatomacese." By 

 J. W. Griffith, M.D., F.L.S. 



In a former paper, it was stated that the markings or dots 

 upon the valves of the Diatomacese, are the optical expressions 

 of depressions existing upon the valves. 



All those authors who have paid special attention to the Diato- 

 maceae, have considered the markings to denote cells ; among these 

 we find Ehrenberg*, Klitzingt, KalfsJ, Smith§, and Quekett||. 



* Die lnfiisioiistliierclien. f Die Bacillarien, and Spec. Algarum. 



t Annals of Nat. History, 1843. § British Diatomaceae. 



II Histological Catalogue of the College of Surgeons; aud Lectures delivered 

 before the College of Surgeons. 



