Cleaveland on Mineralogy and Geology. 397 
to, a provisional arrangement must be adopted, derived from 
a “ well-chosen aggregate of those external characters which 
depend most intimately on the nature of the mineral.” 
The higher divisions are also determined “ by the composition 
of minerals, or by some of their chemical properties.” 
A genus will therefore be composed of certain species, which possess 
some common ingredient, and resemble each other in their chemical pro- 
perties. In selecting the common ingredient, a preference should be given 
to that which is most fixed and permanent. Thus all minerals which are 
composed of lime united to an acid, will form one genus, characterized by 
a common earth, and receiving its name from that earth. 
An order will be composed of certain genera haying bases of 
a similar nature. All the earths have certain common pro- 
perties ; hence all those genera, which have for their base an 
earth united to an acid, will form the order of earthy salts. 
A class is formed by the union of several orders; but the 
relations which unite orders into classes must necessarily be 
more abstract and general than those which exist between the 
several species of a genus, or the several genera of an order. 
The subspecies, varieties, and subvarieties (when necessary), 
are chiefly determined by the external characters. The general 
principles which determine the subdivisions, are, 
1. The presence of any ingredient not essential to the species, but which 
nevertheless produces a considerable change in the specific gravity, fusi- 
bility, or other important properties of the mineral. 
2. Difference of structure, or in the degree of cohesion of the particles ; 
Lag Choma which enable us to recognise all the varieties of carbonate of 
ime, &c. 
3. Colour, when sufficiently constant, though arising from ingredients 
not essential to the species. 
Section 4. Description of Minerals. 
Characters, which would be insufficient to establish a mine- 
ralogical method—that is, a systematic arrangement of minerals 
on certain fixed principles,—may be employed in their descrip- 
tion, by which they are recognised and referred to their true 
place in a system already formed. Hence any character which 
almost uniformly belongs to a particular species, will be useful 
in describing it. 
The primitive form, when ascertainable, should never be 
omitted, nor the accurate measurement of the angles of a crys- 
tal, ‘‘ whether those formed by the inclination of contiguous 
faces to each other, or the plane angles of the faces.” 
The characters should be of easy and expeditious application, 
and the most important should be given first. The geological 
character should always accompany the description, for cer- 
tain minerals are frequently found together, whilst others are 
never associated. The gangue, or matrix, should also be men- 
tioned. ; 
Chapter IV. Nomenclature of Minerals.—The first remark 
on this head is too true to be omitted. 
