REVIEWS. 227 



ogy, and are the essential features of the volume. They, therefore, 

 deserve consideration in some detail. 



The most important feature of a book of this kind is the discussion of 

 ore deposits, yet at the outset a faulty definition of the term "ore" is 

 given. The author says, on page 15, " an ore may be defined as a mineral 

 with a metallic base." Unless further qualified, this definition is, to 

 say the least, vague, for though all ores have metallic bases, there are 

 a number of important minerals with metallic bases which are not 

 ores. Thus, oxide of iron, sulphide of lead, sulphide of copper and 

 other materials have metallic bases, and under proper conditions are 

 ores ; but gypsum, calcite, baryta, mica, and many other minerals have 

 metallic bases and are not ores. Moreover, though many ores are 

 minerals, many others are not minerals at all, but are common rocks 

 having some special metallic constituent as their only unusual feature. 

 Thus the ore of the Calumet and Hecla copper mines is a cupriferous 

 conglomerate, the Mansfeld copper deposits of Germany are cuprif- 

 erous shales, and many other similar instances might be mentioned. 

 The author adds that, "properly speaking, the metallic constituent 

 should be a predominant constituent." Though in some ores the 

 metallic constituent is a predominant one, yet in some of the most 

 important ores the metal forms only a small, and often an insignificant, 

 constitutent. In most gold ores the metallic constituent forms but a 

 fraction of one per cent, of the ore, and in most silver ores the silver 

 forms but a slightly larger amount. In copper deposits, the copper 

 rarely forms a large percentage of the ore, and in many other cases 

 the metallic constituent is entirely subordinate. 



The author states that "the miner considers an ore to be a mineral 

 with a metallic base, occurring in sufficient abundance to be economi- 

 cally valuable ; but from the scientific standpoint, a grain of magnetite 

 in a granite rock is as much an ore as a bed of this mineral." The 

 term ore is essentially a technical mining term, and has no scientific 

 significance whatever. When a metal can be profitably extracted from 

 a certain material, that material becomes an ore ; but other materials may 

 contain just as much of the same metal, and yet, on account of their 

 mineralogical or other features, they may not be commercially profitable 

 sources of the metal, and then they are not ores. Whether a material 

 is an ore or not, is dependent on commercial conditions, which may 

 vary from time to time; and this very fact prevents the term from 

 havins: a scientific meanina^. 



