Miscellanies. 397 
the aggregation of molecules of a particular shape ; -a subject, which 
however curious it may be in general Physics, is nevertheless purely 
hypothetical, and destitute of any bearing whatsoever, upon deter- 
minative or descriptive Mineralogy. 
The relations between the forms of cleavage and crystals, and the 
identity of the former with the primary forms of the species, are 
then pointed out, and practical rules are given for ascertaining the 
primary forms of crystals in all cases. ‘The section concludes with 
a description of the kinds of fracture and surface observable among 
erystals. 
The second section, which relates to compound minerals, com- 
mences with an account of regular composition, or the subject of 
twin-crystals ; after which, irregular composition in all its varieties is 
considered under the following heads:—Group and Geode of crys- 
tals—Iinitative shapes originating in the groups of crystals—Imita- 
tive shapes arising out of the geodes of crystals—Amorphous com- 
position—Accidental imitative shapes—Pseudomorphoses—Irregular 
accidental imitative shapes,—concluding with a description of the va- 
rieties exhibited among the particles of composition, a description of 
single and multiple composition, and the kinds of fracture in com- 
pound minerals. ; 
Section 3rd. relates to the Natural Properties belonging both to 
simple and to compound minerals, and which are divided into Op- 
tical and Physical; the former referring more particularly to the 
mass of minerals, and the latter to their substance. The first con- 
sist of lustre, color and transparency; the second, of the state of 
aggregation, hardness, specific gravity, magnetism, electricity, taste 
and odor. Each of these heads is treated with the requisite degree 
of particularity, but not so as to require any notice here, excepting 
the property of Hardness. This is illustrated according to. the plan 
of Mohs, and with considerable minuteness, it being a property that 
ranks next to crystalline form in the determination of minerals. A 
scale is established for ascertaining the degrees of hardness, by se- 
lecting a certain number of suitable minerals, of which every pre- 
ceding one is scratched by that which follows it, while the former 
does not scratch the latter; and the degrees of hardness are ex- 
pressed by numbers, prefixed to the different individuals of the scale. 
Part II. which consists.of the classification, contains the theoret- 
ical part of the science. It fixes the idea of the species, and treats 
of the princples of classification. After a brief explanation of the 
Vou. XXII.—No. 2. 51 
