AN ESTIMATE OF THE GEOLOGICAL AGE OF THE EARTPL 251 



An interesting fact, however, is in the caseof the potassium revealed 

 as the result of very simple calculation. The present potassium dis- 

 charge of the rivers, if prolonged into the past, as the duration of this 

 is determined b}' the sodium constituent, would have fed into the ocean 

 just about the missing quantity of potassium. The rocks, in short, 

 negative the view commonly urged that the discrepancy between the 

 alkali ratios (sodium : potassium) of rivers and ocean indicates chem- 

 ical differences in the river waters of the past. It is quite the other 

 way. Any alteration of the alkali ratio arising from a change in the 

 potash constituent in the river water of former ages will leave the 

 record of the rocks, while correct for the soda, incorrect for the potash. 



The legitimate deduction appears to be that the potash discharge of 

 the rivers of the past is to be sought for in oceanic deposits and the 

 sediments. This question is briefly considered in this paper. 



One other important factor in the legitimacy of the conclusions 

 arrived at in this paper may be referred to here. The assumption 

 that the early waters of the ocean did not contain the sodium at pres- 

 ent forming so large a part of its total solid contents is supported not 

 only as a deduction of the facts just quoted, but by a consideration of 

 the silicated state of the elements on a lithosphere cooling from fusion 

 and the subsequent effects on such a magma or crust of any probable 

 abundance of acids derived from the chlorine of the ocean, were this 

 free to form hydrochloric acid. It is submitted that such a body of 

 acid vapor and liquid would be neutralized by the various silicated 

 bases, and divided in such proportion among these as would result in 

 what is relatively a small quantity of sodium chloride brought into 

 solution. Our knowledge of the relative abundance of the elements 

 in the earth's lithosphere enables a very definite allowance for this 

 prime v'al action to be effected. 



The consideration of the question of the uniformity in the rate of 

 denudation involves inferences based on the known deficiencies of 

 rainfall in many parts of the earth's surface — the "rainless" regions. 

 Where such exist, there will be elasticity as regards subsidence or 

 upheaval and rate of denudation into the ocean. The first causes the 

 inward retreat upon the land of the watershed defining the oceanic 

 supply, the second its outward advance. But there is no reason to 

 suppose the amount of supply will, on the whole, vary. There is such 

 elasticity to-day to the extent of one-fifth the total land surface of the 

 globe. 



In the next place, the nature of the soils derived from rocks of very 

 various origin enters into consideration. Our existing knowledge shows 

 that there is remarkable uniformity in these, whether derived from 

 igneous or sedimentary rocks. It is in the soils that solvent denuda- 

 tion is chiefly effected. The greater alkali content of the eruptives — 

 leading to their more rapid yield of those substances on first breaking 



