On the Arrangement of Mineral Collections. 233 



I. Is it not the just complaint of almost every student, that he 

 finds his greatest difficulty to be the attainment of the power of dis- 

 tinguishing one mineral from another ; so as readily to ascertain the 

 name or nature of any specimen which falls in his way ? Until he 

 has attained this power of distinction, to what purpose can he avail 

 himself of the knowledge of names, classification and composition ? 

 And is it not the experience of persons who have made greater ad- 

 vances, that this practical difficulty once conquered, the acquisition 

 of the science becomes rather a recreation than a labour ? It is true 

 that, in the chemical arrangement, having the minerals before us, we 

 can compare their natural properties ; but it must often be done by 

 detail, and learned, as it were, by rote. Whereas, by bringing to- 

 gether into orders those which have certain degrees of general re- 

 semblance ; and sub-dividing again, into genera, those having the 

 closest affinities ; the points of discrimination for the species are con- 

 trasted within small compass. The mind soon acquires the leading 

 characters of the orders ; and those of the genera are pretty readily 

 remembered, taking the most characteristic species as the type of the 

 genus. Thus, the species become assorted, in the memory, into 

 small groups ; where their distinctive characters are perceived, with 

 a degree of facility, very different from the complicated selection 

 and comparison of individuals from amongst the 500 species comprised 

 in our systems ; where those having the closest resemblances will 

 sometimes be widely dispersed, and vice versa. 



Suppose the student to have a well characterized specimen, of 

 which he wants to know the name. He finds it easier to ascertain 

 with the aid of a collection, even chemically arranged, than by re- 

 ference only to his books- But he will be likely to find specimens more 

 or less resembling it, in different parts of such a collection, without 

 any efficient guide to the specific distinctions by which he may readily 

 decide between them. But in the natural arrangement he would 

 seldom be long without perceiving the order and genus to which his 

 specimen appertained ; and thus the points of destinction are brought 

 (as above observed), into close contrast. If I am not in error, practical 

 mineralogy would be acquired in Mr. Allan's collection, in half the 

 time it would need in the British Museum. 



It is not to be denied that the natural arrangements has its hitherto 

 unsurmounted difficulties and imperfections, which may be adduced 

 by the advocates for the chemical system ; but I apprehend they 

 will be found both fewer and less important in the former than in 

 the latter. 



II. As to the second objection. The uncertainty of analysis, as a 

 specific distinction, interferes in several ways. 1. The doubtful 

 accuracy of the analyses themselves. 2. The result of Isomerism ; 

 rendering substances analytically identical, different mineral species. 

 3. Isomorphism, whereby substances closely approximating, or even 

 identical in mineralogical character, may be dispersed in a chemical 

 system. 4. The difficulty of deciding, upon fixed principles, under 

 which genus to place, and consequently, where to find certain com- 

 plex minerals. 



1st. In the first case, taking tip a mineralogical book, and observing 



