256 
Thoughts on Miner atogical Systems. 
[Sept, 
Debris, as the word signifies, is formed of the fragments of what was once so- 
lid, and had form. When very much comminuted and mixed together, it is difficult, 
without the aid of chemistry, to detect the different substances of which it consists. 
But in general, and without any very nice chemical examination, we may distinguish 
1 Peat, 
2 Vegetable mould, 
3 Clay, 
4 Sand, 
5 Loam, 
6 Diluvium orgravel. 
Rocks arc divisible into two grand classes; 1st, those having a simple or ho- 
mogeneous aspect ; and 2d, those which appear to be compound. 
Observation teaches us, that the simple rocks are very uniform in character 
in whatever quarter of the globe they are found, and the chemist finds their composi- 
tion equally so. Observation also teaches us, that of the compound rocks the dif- 
ferent parts, where they can be clearly separated, agree also in the uniformity of 
their characters, though derived from the most distant localities. 
These homogeneous substances seem then to constitute the first objects of stu- 
dy. An analytical investigation of rocks naturally fixes our attention on them as the 
last term of the division. Of these every terraqueous substance, not immediately de- 
rived from organic beings, is composed ; and to understand and recognise the former, 
an intimate acquaintance with the latter is indispensable. These homogeneous sub- 
stances are called minerals, and the knowledge of their properties constitutes what 
is called mineralogy, which we may therefore see is but a branch, the alphabet in 
fact, of geology. 
1. It is not every substance which to the eye appears homogeneous, that is to be 
considered a mineral. To constitute a mineral species we must have the same 
simple substances united in the same proportions. It will not invalidate this defini- 
tion to say, that chemistry has often presented us with the same constituents, united 
in the same proportions, for minerals evidently different; and again has differed in its 
analyses of different specimens of what was evidently the same mineral. This is in 
fact but to say, that chemistry as a science is not yet perfect, nor chemists infallible. 
It still remains incontrovertible, that the composition of a mineral is its essence, or 
that which determines it to be what it is and nothing else. If you conceive that 
modified, you must allow its identity gone. Itis no longer the. same thing, and con- 
sequently, not the same mineral species. 
2. Since minerals of different species are found to differ in external characters, it 
is evident, that the latter may be used with due caution as a key to the former. In 
attempting, however, this investigation of the mineral species, we arc to recollect that 
our results must be confirmed by the chemist when doubtful, for we can never pre- 
tend to put the methods in competition. TVe must not exalt the handmaid before 
the mistress. In some instances, however, it must be confessed, that the doubts found- 
ed on a comparison and consideration of external characters have been confirmed 
by a more careful analysis. In fact, to attempt to learn any branch of science by 
a rigid adherence to any one method or principle to the exclusion of every other, is 
to sacrifice knowledge to pedantry, the substance to the shadow. If our object be to 
really know the thing, we must not quarrel with the means. Hauy has justly ob- 
served" L'on peut repondre a ceux qui pensent que la mineralogie doit se suffire a elle 
meme sans avoir besoin de se meler avec des sciences etrangeres, que dans des ope- 
rations si elementaires et que n’exigent q’un si petite depense de moyens ct 
d’effets ;on ne voit proprement ni le chemisteni Ie physicien on n'y voit que le mine- 
ralogists qui interroge la nature d’une manicre plus pressante et plus heureuse.” 
3. A mineral species being once fixed, and its more obvious properties correctly 
described, these will be in general sufficient to enable ns to recognise a specimen 
from a new locality. All those minerals, then, the investigation of which has been 
completed, may be thus recognised; and to effect this successfully we may now pro- 
ceed to consider what are the particulars best fitted for this purpose. 
4. I am here merely speaking of the art of recognising minerals, which may 
thus be seen to depend on the analytical method. The synthetical method arranges 
them in groups of various orders, so as to give a clear and methodical idea of all the 
facts known of their properties, their nature, value, &c. in fact, their history. This 
is of course the more comprehensive part of the subject, but cannot be called the 
most valuable, inasmuch as without the other, it is of no use whatever. It signifies 
little that we know every particular in the history of the diamond, if wo are not qua- 
lified to distinguish It amongst a hundred other substances, It is in fact the founds- 
