622 CROSS, IDDINGS, PIRSSON, WASHINGTON 



which are at present in use for large rock groups, or which were 

 proposed by the author for such groups, are used for the larger 

 divisions, such as Rangs, while those which have at present, or 

 were originally given, narrower or more specific character or 

 application, are used for the smaller divisions, Subrangs, Grads, 

 and Subgrads. 



Inasmuch as few if any of the rock names at present in use, 

 even the broadest, cover the wide mineralogical concepts 

 involved in our proposed Orders, and as it will also be well to 

 make the names of these broad groups quite distinctive, we 

 have adopted as the source of the roots for Orders the names of 

 countries. We have endeavored to select in each case the name 

 of a country where the respective Order is found in especial 

 abundance or is most typically represented, or which is histori- 

 cally connected with the Order. This is, of course, not possible 

 in every case, as some of the most abundant Orders are repre- 

 sented in several countries. In such cases we have endeavored 

 to apportion the ordinal roots equitably among the petrograph- 

 ically prominent nations. 



b) The selection should be based on rocks of which good 

 analyses exist. This is obviously just, since a poor analysis is of 

 little use, and is often of positive harm, to the science and to 

 any system of classification, and furthermore it will frequently 

 happen that a name based on such will prove eventually to have 

 been misapplied. 



c) A locality root already in use should be employed if possible. 



d) As far as is consistent with the preceding principles, the 

 laws of priority will hold good, as usually recognized and as 

 formulated in Dana's System of Mineralogy. 



e) In selecting a new root from several possible localities, 

 the one should be chosen which is best known, has been best 

 described, or which furnishes the most typical material. 



/) The roots should be short, if possible not more than two 

 syllables, and euphonious. 



g) The name of a locality where the mode is normative is 

 to be employed if possible. 



