ROCK CLASSIFICA T10N I I I 



considered more useful to emphasize the characters common to 

 the rocks bearing a common name than those which might dis- 

 tinguish them as individuals. Moreover, it must be admitted 

 that there is need of a systematic arrangement of descriptions 

 of rocks, and that the descriptions of all similar rocks should be 

 found together. 



With the need of systematic classification of descriptions of 

 rocks is an equal necessity for a systematic nomenclature. The 

 present nomenclature is an inheritance of the most fortuitous 

 creations of the earliest investigators, whose knowledge was of 

 necessity often imperfect or faulty, and of recent petrographers, 

 whose suggestions of names have been based on no uniform 

 system. The earlier names have undergone such changes of 

 definition as in more than one case to shift them entirely from 

 their original application. Terms derived from geographical 

 localities, from physical characters, or from mineral compo- 

 nents, have been used indiscriminately. Rocks differing from 

 one another but slightly have in some cases received totally 

 different names, in other cases names alike except for qualifying 

 prefixes. The time has nearly arrived for a complete reformation 

 of petrographic nomenclature. The need is urgent but the con- 

 dition of our knowledge at present is scarcely such as to warrant 

 the immediate attempt to create a systematic nomenclature. 

 When it is devised it should not only be sufficient for present 

 needs, but should be capable of further development along with 

 the growth of our knowledge of the rocks themselves. 



The object of a treatise on igneous rocks should be to convey 

 an idea of the origin and geological history of such rocks, their 

 intricate relationships with one another, and their material char- 

 acteristics. To accomplish this, the known facts may be pre- 

 sented in a number of ways, and the subject may be approached 

 from different directions. Different methods of procedure may 

 commend themselves to different writers, and may be followed 

 with equal success. But there should be one systematic nomen- 

 clature based upon some universally accepted classification. The 

 exact nature of this classification has yet to be determined. 



Joseph P. Iddings. 



