LINOS A AND ITS ROCKS 27 



Classification. — The norm and ratios of the specimen analyzed are 

 as follows : 



Norm Ratios 



Or 6.67 Sal 51.80 



.1 „„ ^^ i^ — = o - =io7- Class III, salfemane. 



Ad 22.01 rem 48.54 



An 20.85 F 49.53 



Ne 2.27 L^TT^^^'-^'- Order 5, gallare. 



^; 9-"^ K.O + Na.O 62 ^ ^ 



01 28.17 ■ 7^~(y "" — =oo3- K.ang 3, camptonase. 



Mt 4.64 ^ ^ 75 



Tl r- K2O 12 



^^ 5-47 ^^T — 7^ = — =0 . 24. Subrang 4, camptonose. 



Ap 1. 00 ^^ ^° 



Rest 0.40 Symbol, TTI. 5. 3. 4. 



100. 74 



From the figures given it appears that this type falls well within 

 all the magmatic divisions, and that it is a typical camptonose. The 

 classificatory influence of the very high magnesia, in which respect 

 it differs most widely from the other rocks analyzed, would be ex- 

 pressed in the minor divisions of the system, especially in the section 

 of grad, which is based on the relations of ohvine to pyroxene. But 

 in the present introductory stage of the new system it is not deemed 

 advisable to carry the classification as far as these minor divisions 

 for ordinary purposes, since the main features of a rock may be quite 

 clearly expressed by the use of the major magmatic divisions alone 

 (from class to subrang inclusive), together with a typal quahfier or 

 adjectival prefixes, to indicate the mode and texture. 



So far as the relations of norm and mode are concerned, the read- 

 justments needed to derive the mode from the norm are of shght 

 importance, being confined chiefly to the augite, the amount of which 

 is small, as we have seen above. The mode may therefore be con- 

 sidered as normative, and the rock may be described as an olivine- 

 phyro-camptonose, which designates very concisely its mode, texture, 

 and chemical composition. In the prevaihng systems of classifica- 

 tion it is an olivine-feldspar-basalt, but the use of a special name 

 would be needed if it were desired to indicate the size and abund- 

 ance of ohvine phenocrysts, in which respects it differs from many 

 others. 



