59§ CROSS, ID DINGS, FIRS SON, WASHINGTON 



ent, more than threefold, nor will it be useful to make in all 

 cases the finer distinctions which obtain in the divisions based 

 on the preponderant group of minerals. 



In Class III, on the other hand, where the femic minerals are 

 equal to the salic, and may in fact exceed them in some cases,, 

 the fivefold subdivision will be employed, and, as far as possible,, 

 the distinctions made in the first divisions of Classes IV and V 

 will be recognized. 



It may be noted here that it appears that in actual practice 

 these later divisions will be used comparatively seldom in Classes 

 II and IV, and it will be remembered that they do not exist in 

 Classes I and V, but that they become important in the inter- 

 mediate Class III. 



Grads are based on the proportions of the standard minerals 

 of the subordinate femic and salic groups in Classes II and IV 

 and of the femic group in Class III. 



For Class II they are: 



Grad i: — — — >- , femic silicate predominant, prepolic. 



„ P + O 5 x femic silicate and non-sili- 



Grad 2 : ' < - > - , . . . . 



M 3 5 cate equal polmitic. 



' -, P + O x femic non-silicate predom- 



Grad 3 : — -± — < - , . v 



M 5 inant, premitic. 



In Class III they are: 



n j P+O 7 , 



Grad 1 : — — — > - , femic silicate extreme, perpohc. 



, P+O 7 5 . , 



Grad 2 : — — — < - > - , femic silicate dominant, dopolic. 



M 1 3 r 



_ , P + O k t, femic silicate and non-sili- 



Grad 3 : — — — < - > - , . ... 



M 3 5 cate equal polmitic. 



P + O x 1 

 Grad 4: — — — < — >— , femic non-silicate dominant, domitic. 



M 5 7 



+ < x 



M 7 



r, , P + O I , . 



Grad 5 : — — - — < - , femic non-silicate extreme, permitic. 



