18 Clarence King — Age of the Earth. 



It therefore appears that no time measure can be deduced 

 from the supposed fixing of the present ellipticity at some past 

 date. 



Astronomical Measure of Earth-Time. 



Croll's hypothesis from which it was proposed to fix dates 

 by secular variations of eccentricity and to correlate the 

 climatic effects of those variations with geological operations 

 and thus measure certain intervals of geological time, required 

 so much questionable physical geography and left so many 

 physical doubts that few have been found to accept the exces- 

 sively complex chain of effects lying between eccentricity data 

 and geological facts. The objections of Professor Newcomb, 

 noticed rather than answered, left Croll's doctrine where it 

 was permissible to believe that there was something in it, but 

 not necessarily that definite sequence of climates which is the 

 core of the idea. 



The gap in Croll's scheme seems to have been successfully 

 stopped by Sir Robert Ball whose interesting proof of the 

 seasonal inequality of the thermal element in climate due to 

 position of the equinoxes, and its intensification in periods of 

 high eccentricity offers a new hope for the accurate dating of 

 at least very modern geological climates. From this point of 

 view late geological history requires reexamination, and if it 

 should appear that a sequence of climates has existed closely 

 paralleling the thermal variations which the astronomical 

 values seem to afford, an extremely probable case will have 

 been made out. And this case would be practically substan- 

 tiated if the hypothesis of H. Blytt should yield the confirma- 

 tion for which he hopes. Blytt* proposes and has already 

 attempted to correlate the secular attractional changes due to 

 varying eccentricity and precession with the observed succes- 

 sive shifting of beach lines. 



So far as he has proceeded it is of interest to note that 

 his time estimates are more in harmony with the physical 

 than the stratigraphical figures. 



Periodic changes in the figure of the hydrosphere relatively 

 to the solid earth, due to alterations of attraction, might be 

 predicted with some confidence if it were clear that the litho- 

 sphere would under the slow stresses involved continue to 

 exercise a degree of rigid resistance comparable with that it 

 opposes to the tidal stress, but there is no proof that it would. 



Since we find the solid earth undergoing slow deformations 

 to-day which are relatively permanent, while its effective 



* The probable cause of the displacement of beach lines. H. Blytt — 1889, 

 Christiania Videnskabs Forhandliuger No. 1 — Additional note 1889 — second 

 additional note 1889. 



