GENERAL STATEMENTS. 1003 



greatly from those given — 0.65 for the shales, 0.30 for the sandstones, and 

 0.05 for the limestones. While with the numbers used discrepancies have 

 appeared, for the most part they are of a kind which throw light upon the 

 processes of segregation of compounds in materials other than shales, 

 sandstones, and limestones. 



In conclusion it is to be remembered that the equations are independent 

 of the estimates of the absolute masses of the sediments, and therefore they 

 can not be said to give any support to the estimates of the average 

 thickness of the sediments for the continental areas, nor to the absolute 

 amounts of the elements which have been calculated to be abstracted 

 from certain of the sediments and segregated in certain others of them. 



Certain of the results set forth in the previous pages indicate the pos- 

 sibility that the estimate of the mass of the sediments as 2 kilometers thick 

 for the continental areas is too large, but it will be noted that this estimate 

 is very conservative as compared with estimates made by others. (See 

 p. 939.) If one were to estimate the mass of the sediments as 1 kilometer 

 thick for the continental areas, while the calculated percentages of the 

 deficiencies and excesses of the various elements in the sediments as com- 

 pared with the original rocks would not be changed, the calculated absolute 

 amounts would be reduced one-half. This would reduce by one-half the 

 calculated percentage of oxygen of the atmosphere required to oxidize 

 ferrous iron (see p. 951), and to oxidize iron sulphide (see p. 952); would 

 divide by 2 the numbers comparing the amount of carbon in the sedi- 

 ments with that in the atmosphere and hydrosphere (see pp. 965-966); and 

 would divide by 2 all absolute estimates of the surpluses and deficiencies 

 of the various elements in the ordinary sediments, as, for instance, the 

 calculated deficiency in iron. (See pp. 987-988.) Other similar changes 

 would be made in the calculations. These facts may be regarded by some 

 geologists as evidence that even the moderate estimate for the sediments of 

 2 kilometers thick for the continental areas is too great, and with this view 

 I am inclined to agree. 



