a 
376 Review of Dana’s Mineralogy. 
of iron, and specular iron. ‘Titanate of iron and specular iron are isos 
morphous and similar physically, yet chemical systems would separate 
the two, and place the former along side of other salts of iron. 
“‘ Besides, various chemical compounds pass into one another by the 
gradual substitution of one isomorphous base for another, and although 
the extremes might be easily arranged in a chemical system, yet the 
transitions are disposed of with much difficulty. The augite family is 
a striking example. 
«A true chemical system should take into consideration the isomor- 
1 
phous relations of the elements or bases, and vient to any one 
set of characters. That element in the compound should be assumed . 
for the ground of distinction, which fixes the peculiar features of the 
ies—the acid in some species, the bases in others. In the vitriols, 
the acid (sulphuric) is the characterizing ingredient; in the alums, sul- 
phuric acid and alumina; and soon. No chemical system can satisfy the 
demands of the science which does not follow nature’s own windings. 
We would not say that the system of Mohs, adopted in this treatise as 
the natural system, is perfect; yet, whether we consider it chemically 
or mineralogically, it will be found to approach more nearly to such a 
system than any other that has been proposed.” 
The tables for determination of species are full, and original 
with the author. We find in the present edition a valuable ad- 
dition to them—the degree of fusibility expressed in numbers 
after the manner of expressing hardness, and also a separate at 
rangement of the species without metallic lustre—according to 
their blowpipe characters. The minerals constituting the scale 
are, 1. Gray antimony,—2. Natrolite,—3. Cinnamon stone, (var 
riety of garnet,)—4. Hornblende, (greenish-black variety,)—. 
5. Feldspar,—6. Chondrodite. The last fuses with difficulty 
on the edges. Jnfusibility is expressed by 7. 
Descriptive mineralogy, (Part VI,) constitutes of course much 
the most bulky portion of the book. From what we have said of 
the elevated character of the introductory chapters of this work, 
the reader may infer that the descriptive part might have suffered 
in the hands of an author who valued so highly speculative a0 
theoretical points. It will however be found, that great care 
and labor has been spent on this portion of the volume. No 
stone has been left unturned. The foreign journals and treatises 
have been ably collated; the species have generally been traced 
to their original authority and all the references authenticated, 
and those only who have wandered in the mazes of foreign a 
ag 
4 
