CLASSIFICATION OF IGNEOUS ROCKS $97 



Since we have to deal here with the two acid radicals CI and 

 SO s , we may distinguish between the sodalite and noselite rocks 

 by dividing Sections 3, 4 and 5 of the fivefold division above, 

 and Sections 2 and 3 of the threefold, on a threefold basis, 

 which appears to be a sufficient subdivision. These Subsections 

 will be as follows : 



prechloric. 



■2 



< - > - , chlorsulphic. 



5 



presulphic. 



Rocks belonging to each of the five Classes here proposed 

 have been fully characterized mineralogically and chemically, 

 as far as the preponderant salic and femic groups of minerals are 

 concerned. There remains the consideration of the subordinate 

 group, femic or salic, in each case, in order to complete the 

 chemico-mineralogical classification of the rocks. 



In Classes I and V since the preponderant group is present 

 in extreme amount, the subordinate group is negligible, and no 

 further division is necessary. 



In Class II the subordinate group is present in notable 

 amount, and is femic, while in Class III the femic group is given 

 second place, after salic, so that in both cases we have to do 

 with femic minerals, and further division will take place in this 

 group and will be in general along the lines laid down in the 

 preceding pages in the description of the divisions from Order 

 to Subrang in Classes IV and V. 



In Class IV the subordinate group is salic and is present in 

 notable amount, so that further division will take place in this 

 group, following the lines of division from Order to Subrang in 

 Classes I, II and III. 



It will furthermore be seen that, since in Classes II and IV 

 the subordinate femic and salic minerals respectively are not 

 equal to the preponderant salic and femic, it will not be neces- 

 sary in these Classes to make the divisions, at least for the pres- 



