XII.] ORIGIN OF METALLIFEROUS DEPOSITS. 221 



of carbonate of soda, is of great significance when taken in 

 connection with the metalliferous character of certain dolomites, 

 which, as we have shown, probably owe their origin to the 

 action of similar alkaline springs upon basins of sea-water." 

 (Ante, page 88.) 



" The intervention of intense heat, sublimation, and similar 

 hypotheses to explain the origin of metallic ores, we conceive 

 to be uncalled for. The solvent powers of solutions of alkaline 

 carbonates, chlorides, and sulphurets at elevated temperatures, 

 taken in connection with the notions above enunciated, and 

 with De Senarmont's and Daubree's beautiful experiments on 

 the crystallization of certain mineral species in the moist way, 

 will suffice to form the basis of a satisfactory theory of metallic 

 deposits." (Ante, page 25.) 



There are about sixty bodies which chemists call elements ; 

 the simplest forms of matter which they have been able to 

 extract from the rocky crust of our earth, its waters, and its 

 atmosphere. These substances are distributed in very unequal 

 quantities, and in very different manners. As regards the fre- 

 quency of these elements in nature, neglecting for the present 

 those which constitute air and water, and confining ourselves to 

 the solid matters of the earth's crust, there are a few which are 

 exceedingly abundant, making up nine tenths, if not ninety-five 

 hundredths, of the rocks so far as known to us. The elements 

 of which silica, alumina, lime, magnesia, potash, and soda are 

 oxides are very common, and occur almost everywhere. There 

 are others which are much rarer, being found in comparatively 

 small quantities. Many of these rarer elements are, however, 

 of great importance in the economy of nature. Such are the 

 common metals and other substances used in the arts, which 

 occur in nature in quantities relatively very minute, but which 

 have been collected by various agencies, and thus made available 

 for the wants of man. It is chiefly of the well-known metals, 

 iron, copper, silver, and gold, that I propose to speak ; but 

 there are two other elements, not classed among the metals, 

 which I shall notice for the reason that their history is ex- 

 tremely important, and will, moreover, enable us to comprehend 



