318 ALBERT JOHANNSEN 



So far as the grouping of the rocks proposed by C. I. P. W. 

 is concerned, it is most admirable, and can hardly be improved 

 upon; it is only upon the rock terms chosen by them that any 

 criticism falls. Teaching the names as selected, it is necessary 

 to impress upon the student that these are only indefinite field 

 terms — and he immediately wants to know the more exact defini- 

 tions. The student who later takes up microscopical work finds 

 — at the present time when the older systems must still be taught, 

 even if supplementary to the newer — that these definitions pro- 

 duce confusion, and he must either "unlearn" the field terms or 

 else originally he must have learned the more exact usage as well. 

 The objection to the latter method is that it makes double work 

 for those students who want only a general megascopic knowledge 

 of the rocks. Had some simple change been made by the authors 

 of the Quantitative System, either in the words used or in their 

 endings, this difficulty would have been overcome. The following 

 substitutes are proposed as expressing, more or less, the fact that 

 the general type of rock represented by the original name is the 

 one preponderating in the group, and for this reason the suffix 

 -eid (from etSo^ "form, appearance") was chosen. As a matter 

 of fact the change proposed is not so great as the spelling would 

 suggest. It is only a change in the pronunciation produced by 

 the substitution of a single letter — from granite to granide, syenite 

 to syenide, etc. The object in using -eid instead of -ide is twofold. 

 It conforms to the derivation of the word, and in those countries 

 where the final e is omitted, the ending ide, changed to id, has the 

 short sound; -eid is everywhere pronounced the same. It will be 

 noted that some of the C. I. P. W. terms are retained, for to such 

 words as phanerite and aphanite there are no objections. For 

 uniformity, however, the same ending is used below in these forms 

 as in the others. 



As divided by the authors of the Quantitative System, so here 

 also the rocks are divided into three main divisions. 



I. Phanereids {$avepo<; } "visible," and elBoi, "form"). Rocks 

 whose different constituents can be seen megascopically. 



II. Aphaneids (acf>avi]<i ; "unseen," and etSo?). Rocks which 

 contain a greater or lesser amount of megascopically indetermi- 

 nable components. These are subdivided into 



