ON ROCK CLASSIFICATION. 



"To class rightly — to put in the same group things which 

 are of essentially the same natures, and in other groups things 

 of natures essentially different — is the fundamental condition to 

 right guidance of actions." These words of Herbert Spencer 1 

 may well form the introduction to this discussion, for they not 

 only declare the importance of right classification, but state 

 clearly in what it consists. It is because of the possibility of 

 losing sight of its actual character in the approaching conflict 

 over the reformation of rock nomenclature, that emphasis is laid 

 at this time upon what seems to the writer to be the true char- 

 acter of rock classification. According to high authority 2 clas- 

 sification is "the act of forming a class or of dividing into 

 classes." And further, a class is defined as "a number of objects 

 distinguished by common characters from all others, a collection 

 capable of a general definition." 



To class rocks rightly would be to put in the same group or 

 class those which are of essentially the same natures, or which 

 may be distinguished by common characters from all others, and 

 which may be capable of a general definition. This leads at 

 once to a consideration of the nature of rocks and of the charac- 

 ters by which they may be distinguished from one another and 

 which may be employed in their definition. 



Nature and characteristics of rocks. — The origin or formation 

 of rocks affects their nature to so great an extent, that it has 

 been made a first basis for their subdivision, resulting in three 

 categories : eruptive, sedimentary, and metamorphic. These, 

 however, do not occupy the same position in the order of for- 

 mation, but may be considered in one case as essentially primary, 

 and in the others as secondary or derivative. The character of 

 the rocks of these three categories, while possessing some points 



1 Man vs. State, p. 5. 2 The Century Dictionary. 



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