Hyland — On some 8pherulitic Rocks from Co. Down. 437 



sitely defined zonal structure. (Paper read before the Eoyal Irish 

 Academy, March 15, 1890. See also Nature, March 20, 1890, 

 vol. xli., p. 469.) 



A " chalcedony, constituting sphericles in a felspar porphyry 

 from the Mourne Mountains," was analysed by Thomas Thomson, 

 with the following result : — 



Silica 95-15 



Alumina, with a little peroxide of iron 1-95 



Lime 2-25 



Water 1-00 



Sp. G. = 2-641 100-85 



(Outlines of Mineralogy, Geology, &c, London, 1836, vol. i., 

 p. 68.) 



