CLASSIFICATION OF IGNEOUS ROCKS 269 



Dosalane ; while Amiatose is the sodipotassic sub-rang of 

 Coloradase, which is the alkalicalcic rang of Britannare, the 

 quardofelic order of the Persalanes. 1 



It is unnecessary to deal here with the still smaller divisions 

 into grades and sub-grades, which are carried out on somewhat 

 similar lines to those of larger size, as they appear to be seldom 

 if ever employed, or with the adjectives which have been devised 

 to indicate the manner in which the " mode " or actual mineral 

 composition differs from the " norm " or ideal composition, for 

 these are matters of entirely subsidiary importance. Nor is this 

 the place to describe the nomenclature to be employed to express 

 the degree of crystallisation, the size of the crystals, and the 

 character of their development ; but I may say that the terms 

 selected appear to be well chosen, and might be conveniently 

 adopted, whatever may be the fate of the quantitative classifi- 

 cation itself. 



The principles of the classification will, however, be more 

 easily understood when they are applied to a particular rock, 

 such as the microgranite already referred to. 



As a result of the calculations that have been made, it will 

 be seen that the gravimetric proportion of salic to femic minerals 

 in the norm or ideal mineral composition of this rock is 95*25 to 

 373, which is more than 7 to 1. The rock is therefore a per- 

 salane. The quartz in the norm amounts to 3176 per cent, 

 and the felspars to 6271, which is less than three-fifths and more 

 than one-seventh. The rock, therefore, belongs to the quardofelic 

 order of the persalane class — an order which, as already stated, 

 has received the name of Britannare. 



The proportion of the molecules of the alkalies, which are in 

 this case all salic, to those of the salic lime is 1 1 10 to 98, which is 

 more than 7 to 1. The rock is therefore peralkalic, and belongs 

 to the Liparase rang of the order. Again, the proportion of the 

 potash to the soda molecules is 537 to 573, which is less than 5 to 3 

 and more than 3 to 5. This places the rock in the sodipotassic 

 sub-rang, which is known as Liparose. 



The calculation of the norm seems long and complicated, 

 but it can, with practice and the help of the tables included in 



1 In the last two classes the matter becomes more complicated. For instance, 

 Marquettose is the domagnesic sub-rang of Marquettiase, the permiric section of 

 Texase, which is the pennirlic rang of Texiare, which again is the pyrolic section 

 of Scotare, the dopolic order of the class Dofemane. 



