998 A TREATISE ON METAMORPHISM. 



potassium, and calcium together, It is seen that this amount is trivial as 

 compared with the total deficiency in the sedimentary rocks, being indeed 

 only 4.02 per cent of this amount. It is therefore plain that, as in the case 

 of magnesium, we must turn to some other direction Jo 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. Many great 

 salt deposits have been discovered in the United States, Europe, and other 

 parts of the world; such deposits are illustrated by those of Poland, New 

 York, and Louisiana. Doubtless many other salt deposits exist which have 

 not been discovered. Moreover it is known that there are extensive salt 

 deposits below lakes such as Great Salt Lake and the Dead Sea. No 

 attempt has been made to quantitatively determine the mass of the salt 

 deposits. Until this is done no statement can be made as to the proportion 

 of the deficiency of sodium in the ordinary sedimentary rocks which such 

 sediments will accoimt for. 



Finally, as is shown on pages 5 J .l-543, in arid regions sodium salts 

 are largely retained in the deposits of the belt of weathering. Since 

 sodium-bearing deposits are known to be very thick in various arid regions, 

 such, for instance, as those in the western part of the United States, the 

 amount of sodium thus accounted for is very great, but as yet our 

 knowledge is not sufficiently advanced to make any quantitative estimate 

 of it. 



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 deficiencv 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 weathering processes and its accumulation in the sea, and which 

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

 Such calculations furnish but another illustration of the danger of consid- 

 ering a single factor in a series of complex geological processes, and 

 neglecting to ask the question whether there are other equally or more 

 important factors concerned. 



When the original rocks containing sodium-bearing minerals are 

 decomposed in the zone of katamorphism, the larger part of the sodium 

 passes into solution, contrasting in this respect, as will be seen, in a marked 



