No. 3.] MACFARLANE— ON CRYSTALLINE ROCKS. 



269 



Mosandritc. 



Licvritc. 



Cordiciite. 



Lepidolite. 



Scaj)oIite, 



Meionite, 



Dipyie. 



Sodalite, 



Hauyn. 



Nobean. 



Lcucite. 



Subsilicntes. 

 Tourmaline. 

 Andalusite. 

 Cyanite. 

 Topaz, 

 Titanite. 

 Staurolite. 



VI. Tcn'.alates, Cohmbates and 

 Tung states. 



Pyrochlorc. 



Tantalite. 



ColuTubite. 



Ytirotantalitc. 



Aeschinitc. 



Poly erase. 



Polymignite. 



Mengite. 



Wolframite. 



VII. Phosphates. 



Apatite. 



Mcnaiite. 



Tryphllite. 



From this list it will be seen that the accidentall3'-occurring 

 minerals in crystalline rocks are five times as numerous as the 

 essential minerals. It is scarcely possible to take a general view 

 of the list without noting not only the number of rare elements 

 which are found among their components, but also the preponde= 

 ranee of bases in their composition. The number of subsilicntes 

 and unisilicates largely exceeds that of the bii^ilicates. The rare 

 tantalatcs, columbates, &c., are exceedingly basic, while no less 

 than ten consist exclusively of anhydrous oxides. Another pe- 

 culiarity in the composition of the silicates among them is the 

 presence of sesqui-oxides in large quantity. Epidote, lievrite and 

 others are silicates of alumina and peroxide of iron, while anda- 

 lusite, cyanite, topaz and many others contain the former base in 

 great abundance. 



With rcQ-nrd to their distribution amono: oriirinal rocks, it is to 

 be remarked that by far the greater number arc native to the 

 coarse grained and schistose series, and occur in largest quantity 

 in their neutral or siliceous families. Granites and syenites are 

 especially rich in them, a remarkable instance being the zircon 

 Byeniteof Fredericksvaern in Norway, in which no le^^s than fifty 

 diflferent minerals are found, among whose components there arc 

 nine rare elcm:>nts. These accessorial minerals become less fre- 

 qut^nt in the porphyritic and trachytic rocks, until among modern 

 hvas very few of them are to b3 found. 



