No. 3.] 



MACFARLANE — OX CRYSTALLINE ROCKS. 



263 



purely his'ic mineral mignctitc nny bs pl;iC3cl, as lithologically 

 rel.itcd, nlonp; with them. The minerals of this class may there- 

 fore b3 c illeJ the b isic essential constituents of rock^^. Wc have 

 thus the following classification of these essential rock minerals. 



Glass 1st.— Fclspathic — Quartz, Orthoclas:, Oligoclase, Labra- 

 dorite, Anorthite, Leucite, Nepheline. 



Class 2nd. — Basic — Potisli mica, Mao-nesia mic:i. Hornblende, 

 Pyroxene, Diallage, Lnstatitc, llyiDcrsthcne, Olivine. Mag- 

 netite. 



The extent to which thesD minerals enter into the constitution 

 of ori.;,inal rocks will ba b^st seen by repeating- here the general 

 view given of the families of rocks, placing at the head of each 

 column the names of the principal constituents. 



Table II. 



General View of the Mineralogical Constitution of the families 



of Oriiiinal Rocks. 



