366 DR T. THOMSON on Asbestus, Chlorite, and Talc. 



constitution of mountain-leather may be represented by the fol- 

 lowing symbol : 



6 (4C + *Af) S 3 + (fM + I/") S 4 + 17Aq. 

 It is obvious that it constitutes a distinct mineral species. 



7. Mountain-Cork. 



The specimen of this mineral, selected for analysis, was from 

 Piedmont ; but I do not know the exact locality. 



Its colour was light buff: it was composed of fibres so fine 

 as to be scarcely visible before a common magnifying glass. 



It was soft enough to be indented by the nail : it had the 

 same elastic feel which characterizes common cork. 



Lustre silky ; nearly dull ; opaque ; very tough. Specific- 

 gravity 2.442. 



Before the blowpipe fuses into a black glass. When heated 

 to redness it loses 1.2 per cent, of its weight, which is pure wa- 

 ter, and assumes a dark brown colour. 



Its constituents, after ignition, were found to be as follows : 



Silica, .;; ....;>'. .... . 51.75 



Lime, . . .. >^.;'rii 14.05 



Magnesia, ..... 10.85 



Protoxide of iron, ; ' : : , } . 1 8.90 

 Alumina, . . . j.u'yti 1-95 

 Protoxide of manganese, 1 .85 



99.35 



