268 SCIENCE PROGRESS 



molecular proportion, in the salic minerals, of the alkalies to 

 the lime. 



1. K ^ + Na,.Q > _7 peralkalic , K 2 + Na,0 < ^ > 3_ alkalicalciCj 



CaO i J CaO 3 5 



K 2 + Na..O 7 5 , „ ,. K,0 + Na.,0 3 1 , , • 



2. — — t^—x — — <— >— domalkalic. 4. — = — J, ^ - <^->— docalcic. 



CaO 1 3 ^ CaO 5 7 



„ K.,0 + Na.,0 1 , . 



5. - Ca0 - < yP ercalac. 



Each of these rangs is again split up in exactly similar 

 fashion into five sub-rangs, according to the molecular proportion 

 of the salic potash to the salic soda. In the last two classes 

 the rangs and sub-rangs are based on the molecular proportions 

 of the bases in the femic minerals. 1 



The division into classes and orders 2 is based on gravimetric 

 calculations — that is to say, it is determined by the ratio of 

 the total weights of the groups of minerals on which the 

 classification depends ; but in forming the smaller divisions, the 

 rangs and sub-rangs, it is the molecular proportion of certain 

 chemical constituents that is considered. It is difficult to find a 

 logical justification for this fundamental change in the basis of 

 classification. Again, it is not the whole of the chemical con- 

 stituents in question that determines the classification, but only 

 so much as forms part of the salic or femic minerals, as the case 

 may be. For instance, the lime in the femic minerals has no 

 influence on the division into rangs in the first three classes, 

 only that in the salic minerals being taken into consideration, 

 while in the subdivisions of the other two classes only the femic 

 lime is considered. 



Both rangs and sub-rangs receive distinctive names taken 

 from localities where typical rocks are met with ; the former 

 end in -ase, the latter in -ose. It is the name of the sub-rang 

 which appears to be generally employed when referring to a 

 rock. 3 



As specimens of the nomenclature, it may be mentioned that 

 Essexose is the dosodic sub-rang of Essexase, which is the 

 domalkalic rang of Norgare, the lendofelic order of the class 



1 There are also sections of rangs and of sub-rangs with which we need not 

 concern ourselves here. 



2 As well as that into sections of orders and sub-orders in the last two classes. 



3 See note, p. 269. 



