Geology and Mineralogy. 255 



It is found that silica shows an excess of 3*2 per cent in the 

 secondary rocks and alumina a deficiency of 3*7 per cent. The 

 author suspects that this discrepancy is largely due to errors in 

 the determination of the silica and alumina in the analyses of 

 shales. 



Some of the general conclusions in regard to carbon are alread}^ 

 somewhat familiar through the work of Chamberlin and others, 

 the amount which is locked up in the sedimentary rocks being 

 estimated at many hundred times that contained in both the 

 atmosphere and hydrosphere. 



" The chief processes which abstract carbon dioxide from the 

 atmosphere are those of carbonation and the building up of car- 

 bonaceous deposits. All the replenishing processes, including 

 the reversing processes of silication and the oxidation of buried 

 carbon compounds, have been barely able to keep a minute por- 

 tion of the carbon dioxide in the atmosphere. ... It is probable 

 however that the work of man, especially during the last half 

 century, has returned a great volume of carbon dioxide to the 

 atmosphere by the artificial oxidation of carbonaceous material, 

 and thus has reversed the average of the processes of nat-ire, 

 which plainly appear to have caused depletion of the carbon 

 dioxide in the atmosphere. In consequence, at the present time 

 the amount of carbon dioxide in the atmosphere may be increas- 

 ing rather than decreasing." 



In treating of the alkalies it is shown that the amount of 

 potassium in the sedimentary rocks and the ocean agrees fairly 

 well with the proportions in the original igneous rocks. In the 

 case of sodium, however, there is a remarkable deficiency in the 

 sedimentary rocks, and even when the salt of the ocean is added 

 the total sodium reaches a proportion not more than one-third of 

 that in the original rocks. 



"It is, therefore, plaiu that we must turn to some other direc- 

 tion to account for the great deficiency of sodium in the ordinary 

 sedimentary rocks. The natural direction to which to turn is to 

 the salt deposits of the world. . . . 



" From the foregoing it appears highly probable that we must 

 look to the salt deposits and to the alkaline deposits of arid 

 regions to explain the great deficiency of sodium in the ordinary 

 sediments rather than to the ocean. If this conclusion be correct, 

 calculations upon the age of the earth have no value which are 

 based upon the derivation of salt from the land through weather- 

 ing processes and its accumulation in the sea, and which ignore 

 or place as relatively unimportant the salt deposits of the land." 



The final chapter of 240 pages deals with ore deposits and is an 

 amplification and further systematization of the papers already 

 published by the author in the Transactions of the American 

 Institute of Mining Engineers. Special emphasis is placed on 

 the application to ore deposits of all laws developed for meta- 

 morphism in general. 



The foregoing pages of this review have served to give some 



