2 SMITHSONIAX MISCELLANEOUS COLLECTIONS VOL. 56 



A faultless mode of arriving at the ocean's age is perhaps unattainable, 

 though better ways than are now available may possibly be elaborated 

 hereafter. All that can be hoped for at present is that diverse methods 

 may lead to estimates of the same order of magnitude ; and such a result 

 is more important just now than ever before. By physical reasoning 

 geologists have been compelled to adopt a moderate estimate of geological 

 time. Of late, however, physicists engaged in studies of radioactivity have 

 reached the conclusion that certain uranium minerals are of an enormous 

 age, which is estimated by simple though tremendous extrapolation. If 

 geologists can now give convincing reasons for adhering to ages within a 

 hundred million years, or even within two hundred, they may partly repay 

 the heavy debt due by them to Kelvin and his intellectual heirs. 



So long ago as 1860 John Phillips,^ the originator of the mechanical 

 theory of slaty cleavage, estimated that the time required for the deposi- 

 tion of the stratified rocks lay between 38 and 96 million years. So far as 

 my reading goes, this was the only reasonable estimate prior to Kelvin's 

 truly epoch-making paper of 1862.^ During the last 20 years much energy 

 has been expended upon the study of the maximum thickness of strata 

 and the time-rate of their deposition. In 1890 de Lapparent thus esti- 

 mated a period of from 67 to 90 millions of years.' The most careful 

 investigation of this kind yet made is due to Mr. Charles D. Walcott who, 

 in 1893, carried out minute and cautious studies of the rate of deposition 

 and of the amount of accumulation, both mechanical and chemical.^ His 

 estimate for the lapse of time since the base of the Cambrian is 27,640,000 

 years and he allows for the Algonkian a period of 17,500,000 years. As a 

 matter of course this last figure rests on extremely imperfect data and 

 should probably be increased. Mr. Walcott considered 70 millions the 

 maximum age. In 1899 Sir Archibald Geikie stated that, so far as he 

 was able to form an opinion, 100 million years would suffice for the forma- 

 tion of the stratified rocks,° and in 1900 Mr. W. J. Sollas, assuming a 

 constant rate of deposition, reached an age of 26-J million years.* . In 

 1909 Mr. Sollas increased this estimate to nearly 34 million years,'' but in 

 view of erosions and the uncertainties involved he inclines to believe, as 

 do many others, that the pre-Cambrian sediments took as much time for 

 their deposition as those from the base of the Cambrian to the top of the 

 column. Making also an allowance for gaps, he thinks the stratigraphical 

 column, if complete, might indicate 80 million j^ears. He draws especial 



1 " Life on the Earth," etc., 1860, p. 119. 



2 Trans. Roy. Soc' Edinburgh and Thomson and Tait, Nat. Phil., Pt. II, p. 46S. 



3 Bull. Soc. Geol. de France, vol. 18, 1890, p. 351. 

 * Journal of Geol., vol. 1, 1893, p. 675. 



» Brit. Assoc. Adv. Sci., 1899, p. 727. 

 « Brit. Assoc. Adv. Sci., 1900, p. 711. 



' Mr. Sollas assumes a constant rate of deposition of one foot per century and thinks most 

 geologists would incline to a higher rate. Quart. Jour. Geol. Soc. London, vol. 65, 1900, p. CXII. 



