JoLY — An Estimate of the Geological Age of the Earth. 27 



potassium. The rocks, in short, negative the view commonly urged, that the dis- 

 crepancy between the alkali ratios (sodium : potassium) of rivers and ocean 

 indicates chemical 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 bo 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 present 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 vapour and liquid would be neutralised 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 primaeval 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 waterslied defining tlie 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 denudation is chiefly effected. The greater 

 alkali content of the eruptives — leading to their more rapid yield of those 

 substances on first breaking down — is probably compensated by their physical 

 character, in many cases conferring greater durability upon them. These and 

 other considerations lead to the view that there is no sufficient evidence to ascribe 

 greater alkali content to the rivers of the past. 



The origin of the interstratified beds of Rock Salt, the solvent-denudation of 



