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SCIENCE 



[N. S. Vol. XXVIII. No. 726 



opposed to the view that the radio-activity 

 and crustal disturbance are connected, are 

 in its favor. For while those rich areas 

 testify to the supply of radio-active ma- 

 terials, the slow rate of growth prevailing 

 deprives those deposits of that character- 

 istic depth which, if I may put it so, is of 

 more consequence than a high radio-ac- 

 tivity. For the rise in temperature at the 

 base of a deposit, as already pointed out, 

 is proportional to the square of the thick- 

 ness ; in reality the dilution of the supplies 

 of uranium which reach the calcareous 

 oozes flooring the disturbed areas is a neces- 

 sary condition for any effective radio- 

 thermal actions. 



It might appear futile to consider the 

 matter any closer where so little is known. 

 But in order to give an idea of the quanti- 

 ties involved I may state that, if my cal- 

 culations are correct, a rate of deposit com- 

 parable with that of the chalk prevailing 

 for ten million years would, on assumptions 

 similar to those already explained when 

 discussing the subject of mountain-build- 

 ing, occasion a rise of the deeper isogeo- 

 therms by from 20 to 30 per cent, of their 

 probable normal depth. 



In making these deductions as to the in- 

 fluence of radium in sedimentary deposits, 

 I have so far left out of consideration the 

 question of the time which must elapse in 

 order that the final temperature-rise in the 

 sediments must be attained. The question 

 we have to answer is : Will the rate of rise 

 of temperature due to radium keep pace 

 with the rate of deposition, or must a cer- 

 tain period elapse after the sedimentation 

 is completed to any particular depth, before 

 the basal temperature proper to the depth 

 is attained? 



The answer appears to be, on an approxi- 

 mate method of solution, that for rates of 

 deposition such as we believe to prevail in 

 terrigenous deposits— even so great as one 



foot in a century, and up to depths of accu- 

 mulation of 10 kilometers and even more — 

 the heating waits on the sedimentation. Or, 

 in other words, there is thermal equilibrium 

 at every stage of growth of the deposit; 

 and the basal temperature due to radio- 

 active heating may at any instant be com- 

 puted by the conductivity equation. For 

 accumulations of still greater magnitude 

 the final and maximum temperature ap- 

 pears to lag somewhat behind the rate of 

 deposition. 



From this we may infer that the great 

 events of geological history have primarily 

 waited upon the rates of denudation and 

 sedimentation. The sites of the terrige- 

 nous deposits and the marginal oceanic pre- 

 cipitates have many times been convulsed 

 during geological time because the rates of 

 accumulation thereon have been rapid. The 

 comparative tranquility of the ocean floor 

 far removed from the land may be referred 

 to the absence of the inciting cause of dis- 

 turbance. If, however, favorable condi- 

 tions prevail for such a period that the 

 local accumulations attain the sufficient 

 depth, here, too, the stability must break 

 down and the permanency be interrupted. 



Upheaval of the ocean floor, owing to the 

 laws of deep-sea sedimentation, should be 

 attended with effects accelerative of deposi- 

 tion—a fact which may not be without in- 

 fluence. But although ultimately sharing 

 the instability of the continental margins, 

 the cycle of change is tuned to a slower 

 periodicity. From the operation of these 

 causes, possibly, have come and gone those 

 continents which many believe to have once 

 replaced the wastes of the oceans, and which 

 with all their wealth of life and scenic 

 beauty have disappeared so completely that 

 they scarce have left a wreck behind. But 

 those forgotten worlds may be again re- 

 stored. The roUed-up crust of the earth is 

 still rich in energy borrowed from earlier 



