3G Dr. Mac Culloch on 



association of such mineral characters with certain geological 

 relations were constant, a geological arrangement would serve 

 all the purposes of a mineralogical classification, or the latter 

 would equally perform the functions of both ; but to render 

 the arrangement absolute and unexceptionable, the geological 

 order of nature should itself be also constant. 



The mineralogical method of classifying rocks is, however, 

 not only imperfect, even in its own internal mechanism, but is 

 at perpetual variance with the geological one, as I have fully 

 shown in that work which treats of the Classification and De- 

 scription of Rocks. It is therefore not only useless, even for its 

 own declared objects, but is pernicious when adopted for geo- 

 logical purposes ; for which cause it was there rejected. 



But as I have there also shown that a constant general 

 peculiarity of mineral character is attached to each of the 

 geological divisions of rocks, a geological arrangement, imper- 

 fect as it is, and as it probably ever will be, is not only as 

 valuable as a mineral one for the mere distinction of rock 

 specimens, but, in some cases, preferable \ while it is decidedly 

 superior as it relates to the investigation and study of nature. 



The very basis of the study of geology is the knowledge of 

 rocks ; but that knowledge is of little value for any other pur- 

 poses but the study of geology. The mere mineralogist may 

 be permitted to adopt a mineralogical arrangement ; he ought 

 indeed to do so ; because, to him, rocks are but the reposito- 

 ries of minerals. 



The classifications which I am about to describe have 

 either been intended for the purpose of facilitating the study 

 of geology, or they have been considered as a branch of the 

 science, a declaration of the order and arrangements of nature. 

 Thus, they may be imagined to be either artificial or natural. 



A principle of arrangement, some kind of logic, good or bad, 

 seems to be an inherent propensity in the human mind ; but, 

 while the sound reasoner adapts his logic to nature, the pro- 

 position is more commonly reversed, and nature is tortured 

 into forms, against which she rebels. But as it is one of the 

 qualities of a system to assimilate every thing to itself, an 

 artificial arrangement soon comes to be considered as a natural 

 one ; and when even its inventor learns to see only through 



