798 WHITMAN CROSS 



The natural reply to all such criticisms is mainly a reference to 

 certain principles which must be recognized in any systematic 

 classification of igneous rocks. Fermor clearly desires a method of 

 classification specially adapted to the peculiar "Kodurite Series," 

 the rocks he happens to be working with. But a local or provincial 

 "series" is not and cannot be made a broad systematic concept. 

 Such a series has certain features or characters common to other 

 series, but that which specially characterizes a local series is surely 

 not a factor to be prominently introduced into systematic classi- 

 fication of rocks in general. Any comprehensive system must 

 recognize first the factors which are important because common to, 

 though variable in, many rocks, and later take up those which are 

 notable in addition as distinguishing a few. 



General petrographic system must bring out through classi- 

 fication the relations of kodurite to other rocks, as well as its pecul- 

 iarities. The hypothetical kodurite has other notable chemical 

 characters besides its manganese contents. It is assumed to be 

 remarkably rich in potash and poor in soda; rich in lime and poor 

 in magnesia. It is these characters that show the relation of such 

 a type to other rocks, not the unique richness in manganese. To 

 express these broader relations is the object of systematic classi- 

 fication, and it is these factors of general chemical relationship 

 which are logically applied in the Quantitative System. 



An igneous rock having the composition assumed for kodurite 

 would be a new and interesting magmatic variety irrespective of 

 its manganese, through its quite abnormal association of high lime 

 and potash with low magnesia and soda. The Boirani kodurite 

 possibly falls in another perpotassic subrang, of higher hme con- 

 tents even in its salic molecules, and still more markedly calcic in 

 its femic constituents, than kodurite proper. These facts are just 

 what a logical system should bring out before the unusual richness 

 in manganese finds expression. No system can be constructed 

 permitting the application of each of the many chemical elements 

 of igneous rocks in accordance with its order of prominence in each 

 case, now first, now fifth, now tenth. 



From this point of view the fact that the unusual richness 

 of the Kotakarra kodurite in manganese finds expression in the 



