248 



THE CANADIAN NATURALIST. 



[Vol. vi. 



.tuents. They are sometimes made up of tlio same common 

 chemical components as the essential rock constituents, but much 

 more frequently other r.nd rarer elements enter into their compo= 

 sition. It is indeed almost exclusively from these accessorial 

 minerals that many of the rare simple elements have been derived 

 with which chemists alone have any intimate acquaintance. Thus 

 glucinum, cerium, yttrium, lanthanium, columbium, tantalum, 

 tun^^sten a.nd zirconium are only found as components of accessorial 

 rock constituents, while o'.her elements, such as sulphur, phcspiio- 

 ru5, boron, fluorine, chlorine, tin, copper, lead, chromium and 

 titanium are frequently found in thorn, which but rarely occur in 

 • csscnlial rock constituents. The following' is a catidojiue of the 

 accessorial constituents of rocks, arran<red accordinc: to Dana's 

 system, which at the iamc time indicates briefly their chemical 

 nature. 



I. Kaiive elements. Ferofskite. 



Spinellc. 



Gold. /, ., 



Gahnito. 



bilver. 



Chromite. 



Mercury. 



Chrysobervl. 



Iron. _. \ 



^ , Tinstone. 



Diamond. _ ,., 



, .^ Eutile. 



Graphite. 



II. Sulphides, ^c. 



Molybdenite. 

 Galena. 

 Blende. 



Magnetic pyrites. 

 Iron pyrites. 

 Copper pyrites. 

 Bkuterdite. 

 Cobalt ite. 

 Leucopyrite. 

 Mi.spickel. 



III. Fluorides. 



Fluorite. 

 Fluocerite. 



IV. Anhydrous Oxides. 



Corundum, 



Hematite. 



llmenitc. 



V. Anhydrous Silicates. 



1. Bi silicates. 



Acgirite. 



Acmite. 



Spodumcne. 



Crocidolite. 



Beryll. 



Eudialite. 



2. Uni silicates. 



Leucophanite. 



Wohlerite. 



Phenakite. 



Helvinc. 



Zircon. 



Vesuvianite. 



Melilite. 



Epidote. 



Sanssuritc. 



Allanite. 



Gadolinite. 



