(md Mineralogy. ‘iSJl 
and the third magnetic pyrites.. Let this genus be considered 
as a fixed point, and collect around it such species (already 
united into genei’a,) as possess the greatest similarity with the 
species contained in it. It is clear enough that this junction 
must not be founded on the mere superficial appearance, but on 
a comparison of all the natural historical properties they possess^ 
The species collected will be arsenical pyrites, copper-nic- 
kel, tin-pyrites, and copper-pyrites. If we endeavour to join 
more species with those already enumerated, it will be found to 
be impossible, unless we choose again to destroy the relation, 
which has arisen from the juxtaposition of the preceding spe- 
cies, and hitherto maintained a definite sphere of union. Let 
us farther select lead-glance : To this grey antimony, molybdena, 
black tellurium, vitreous silver, bismuth-glance, will unite them- 
selves. Select the genus of iron-ore : To this grey manganese- 
ore, chrome-ore, cerium-ore, titanium-ore, tin-ore, wolfram, and 
others, unite themselves ; and being properly divided into 
genera, these substances will exhibit well defined groups, which 
correspond exactly to the natural families in the vegetable king- 
dom, and which, springing from the same principles as those 
families, are consequently of equal use with them m the natu- 
ral system. 
50. Idea of an order. — The union of such genera is founded 
on a particular degree of natural historical similarity (39.)? the 
closest after that from which the genera originate (41.) The 
collection of genera united by this degree of similarity is nam- 
ed an order. 
51. Its Universality. — This idea of natural physistorical orders 
may be extended through the whole mineral kingdom. Hence, 
there is no genus which does not extend under some order, as there 
is no species wdiich does not stand under some genus. The re- 
gularity and uniformity of the system requires it to be so. Yet 
the fixing of those orders in such a manner as to be applicable 
and conformable to nature, is attended with difficulty; just as 
difficulties occur in effecting this for botany. An attempt to 
attain this object will be exhibited afterwards. We must look 
to futurity for improvement. 
52. Traces of this idea in the older Mineralogy. — The idea 
of natural historical orders in the mineral kingdom, appears to be 
VOL, in. XO. b. OC'TOBKR 1820. 
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