562 CROSS, IDDINGS, PIRSSON, WASHINGTON 



present systems are to a large extent arbitrary aud subjective, 

 and are capable of being applied differently by different individu- 

 als, as is evident from the numerous cases where different names 

 have been given to the same rock, or the same name to obvi- 

 ously different rocks. 



2. There is a lack of uniformity in the method of application 

 of existing systems not only among petrographers of different 

 countries, but among those of the same country. 



3. The present systems are to a certain extent founded on 

 theory or hypothesis, while classification in order to be stable 

 must eschew all such bases,, and be founded only on ascertained 

 facts. 



4. Present systems are to a large extent qualitative rather 

 than quantitative, the result being that some given character of 

 rocks is arbitrarily used as a criterion beyond its natural range 

 of application, as, for example, the use of the mere presence of 

 feldspar to distinguish a group of rocks, whether it be the domi- 

 nant constituent or only a very subordinate one. 



5. The construction of modern systems is faulty in that the 

 groups of rocks, or of rock families, now recognized are quite 

 inadequate to express known relationships, and the varying 

 groupings used by different authors are not based upon definite 

 principles, nor are the principles applied uniformly. As a result 

 of this condition, existing systems are highly uneven and it is 

 often necessary to use either too specific or too general terms in 

 naming a given rock. 



6. The nomenclature of petrography is quite inadequate to 

 express the relations between the various groups. The single 

 termination makes it impossible to indicate in the name, per se, 

 whether it applies to a large or to a small classificatory division, 

 or whether to rocks or minerals, and gives rise to great monotony. 



7. As a consequence of these conditions, there is no guide as 

 to when the use of a new name is necessary or justified, each 

 investigator being his own judge in such matters. In some rock 

 groups which have been recently studied, there is an abundance 

 of new names, while in other more common and longer known 



