Joty—An Estimate of the Geological Age of the Earth. 27 
potassium. ‘The rocks, in short, negative the view commonly urged, that the dis- 
erepancy 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 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 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 Harth’s lithosphere enables a very 
definite allowance for this primezeval 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 
EHarth’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 willon 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 
