Clarence King — Age of the Earth. 19 



elastic resistance to tidal stress is sufficient to permit a water 

 tide, it appears that either the purely telluric stresses are 

 greater than the moon's attraction, or that there is for the time 

 rate of application of equal stress, a transitional value above 

 which the elastic resistance of the earth-solid is enough to con- 

 serve figure, and below which plastic deformation is easy ; 

 a relation of properties such as Kelvin suggests for ether. 

 Under the former alternative, deformations due to purely 

 telluric forces might by upheaval or subsidence at any time 

 mask or counteract astronomical beach shifting. In the latter 

 case to make use of the astronomical data for displacement of 

 beaches, it is required to ascertain the time rate of terrestrial 

 plasticity accurately enough to know that relatively to the dur- 

 ation of eccentricity and precession cycles and their correlative 

 attractional variations, the reaction of the lithosphere would 

 differ enough from that of the hydrosphere to allow of the 

 beach shifting sought. 



Beyond the most modern geological dates the grander earth, 

 deformations have carried ancient beach lines out of all recog- 

 nizable radial relations with each other and the several oceans 

 of which they mark the shores, or else as is frequently the 

 case with rising continents they have been wholly effaced by 

 erosion. Evidently the Croll-Blytt time measure, interest- 

 ing as it may prove to be for recent dates, is at present inap- 

 plicable to any general determination of the earth's age. 



Earth-age measured by Sun-age. 



• 



Since the incrustment of the earth would be almost imme- 

 diately followed by a climate controlled wholly by the sun's 

 heat, redistribution of the crust by water necessitates a sun 

 heat received upon the earth's surface sufficient at least to 

 maintain the temperature above that of permanent freezing. 



Newcomb* remarks : 



"If we reflect that a diminution of the solar heat by less 

 than one-fourth its amount would probably mean an earth so 

 cold that all the water on its surface would freeze, while an 

 increase of much more than one-half would probably boil all 

 the water away, it must be admitted that the balance of cause 

 which would result in the sun radiating heat just fast enough 

 to preserve the earth in its present state has probably not 

 existed more than 10,000,000 years." 



All we know of the earlier strata indicates a water mechan- 

 ism for the denudation, comminution and deposition of rock. 

 Exactly the division of this work between tidal and river 



* Popular Astronomy, p. 511. 



