376 Review of Dana's Mineralogy. 



of iron, and specular iron. Titanate of iron and specular iron are iso- 

 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- 

 phous relations of the elements or bases, and not be subservient 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 

 species — 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 so on. 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 ar- 

 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, (va- 

 riety of garnet,) — 4. Hvmblende, (greenish-black variety,) — 

 5. Feldspar, — 6. Chondrodite. The last fuses with difficulty 

 on the edges. Infusibility 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 and 

 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 au- 



