included, though care was taken in choosing the sample, it 

 is not impossible that it contains some basalt, which is rich 

 in alumina. A certain amount of alumina is present, of 

 course, in the spinel of the diallagite. The high percentage 

 of quartz and carbonates in the Norton's Basin rock shows 

 it also is impure. Mr. Card specially remarks on the 

 difficulty of selecting a specimen free from secondary 

 minerals. 1 The analyses shows that even after careful 

 choice some carbonate was included. 



Perhlotites. 



The peridotites are those rocks which contain predomin- 

 antly olivine, with lesser amounts of pyroxene with spinel 

 or chromite. Three types occur in the Dundas quarry. 



Liiersolite. — This rock contains about forty-five or fifty 

 per cent, of olivine, the remainder being made up of ensta- 

 tite and diopside, the former slightly in excess, with a 

 small amount of picotite. The alterations are those 

 described previously. Particularly noticeable is the pilite 

 (matted actinolite replacing olivine) which occurs in long 

 bands in the rock, and in which is embedded perfectly fresh 

 pyroxene. 



Ha rzburgite— This is composed of about seventy per 

 cent, of olivine, with the remainder chiefly eustatite, a 

 little diopside and brown picotite. This is more common 

 than lherzolite. The alterations are a described above. 



Dunites occur composed of olivine with very subordinate 

 amounts of pyroxene, and always a percentage of picotite. 

 A fairly fresh specimen was analysed with the following 



