258 Dr T. THOMSON'S Account of the 



session, which is of considerable size, I got from my friend and 

 former pupil Dr SCOULER ; who some years ago passed a summer 

 on the north-west coast of America, between Nootka Sound and 

 Columbia River ; and, among many other natural productions of 

 the country, he brought home specimens of this pipestone. He 

 procured it from the Indians, and was ignorant of the part of the 

 country where it occurs, or the kind of rock with which it is as- 

 sociated. 



It constitutes an amorphous compact stone, through which a 

 few scales of mica are scattered, having much the appearance of 

 claystone ; but softer. 



Fracture earthy. 



Colour light-greyish blue. Powder very light smalt blue. 



It is rather harder than gypsum; but soft enough to be 

 scratched by the nail. Sectile. Opaque. 



The particles, when scraped off with a knife, feel gritty be- 

 tween the teeth. 



Specific gravity, 2.606. 



It does not melt per se before the blowpipe. 



Mr THOMAS MUIR made an analysis of it at my request, and 

 found the constituents to be 



Silica, ..... 55.620 



Alumina, . . . . 17.208 



Soda, ..... 12.160 



Peroxide of iron, . 7-612 



Lime, 2.256 



Magnesia, .... 0.112 



Water, .... . 4.600 



99.568 



It consists of four silicates ; namely, of alumina, soda, peroxide 

 of iron, and lime. Were we to consider the bisilicates of iron 



