III.—Chapters on the Mineralogy of Scotland. Chapter Sixth.— 
“Chloritic Minerals.” By Professor HEDDLE. 
(Read 3d March 1879.) 
“CHLORITIC MINERALS.” 
There is no department of natural science which is so defective in its general 
scheme of arrangement as mineralogy ; and its sectional grouping is, if possible, 
still more defective. 
Such correlations as are expressed by the terms, “the Micas,”—“ the 
Felspars,’—“ the Garnets,” &c., are only admissible if the substances united 
in such groups are included under one general formula, and function in a more 
or less similar manner as rock-formers. 
Under such methods of arrangement as are in vogue, many substances are 
left to stand isolated as intermediates,—substances which frequently form im- 
portant integers of a regular sequence. And when such groups are constituted 
upon the possession of merely some one general feature, it almost invariably 
results that there are linked together substances which have nothing else in 
common. 
Mineralogy presents numberless examples of the misleading effect of being 
guided by mere externals ; and the more the geognostic relations of minerals are 
sought out, the more clearly do we see the false conclusions into which we are 
drawn when we are guided by externals alone. 
To no group does this perhaps apply more emphatically than to that of the 
“ Chlorites.” Of the twelve minerals which in our systems find a place therein, 
some are the products of mere solution, some of direct chemical change, some of 
metamorphic transmutation. Of these, some are found in sedimentary rocks, 
some in volcanics;—in limestone, in serpentine, in schists, in granite, and in 
traps. 
The extreme injudiciousness of founding a natural history group upon so 
trivial a character as colour alone, is shown by the laxity which has gradually 
crept in—by the expanding as it were of the name into “ the chloritic group,” 
or “ chloritic minerals.” 
From the difficulty of discriminating between several substances which fall 
under such a term, there can be no doubt that the term has not unfrequently 
been adopted as a convenient cover for ignorance. 
“T always say chloritic mineral when any of my students ask me what they 
are; it covers a vast amount of ignorance.” This was the remark made to 
me by a teacher of geology when we were discussing the green substances 
VOL. XXIX. PART I. P 
