THE BIRTH-TIME OF THE WORLD 4 7 



sediments we have assurance of the continuous exposure of the 

 continents above the ocean surface. The doctrine of the per- 

 manency of the continents has in its main features been accepted 

 by the most eminent authorities. As to the actual amount of 

 land which was exposed during past times to denudative effects, 

 no data exist to show it was very different from what is now 

 exposed. It has been estimated that the average area of the 

 North American continent over geologic time was about eight- 

 tenths of its existing area. 1 Restorations of other continents, so 

 far as they have been attempted, would not suggest any more 

 serious divergency one way or the other. 



That climate in the oceans and upon the land was through- 

 out much as it is now, the continuous chain of teeming life and 

 the sensitive temperature limits of protoplasmic existence are 

 sufficient evidence. 2 The influence at once of climate and of 

 elevation of the land may be appraised at their true value by 

 the ascertained facts of solvent denudation, as the following table 

 shows. 



Tonnes removed in M elevatiou 



solution per square M 



mile per annum. 



North America . . . -79 700 



South America . . . .50 650 



Europe ...... 100 300 



Asia 84 950 



Africa 44 650 



In this table the estimated number of tonnes of matter 

 in solution, which for every square mile of area the rivers 

 convey to the ocean in one year, is given in the first column. 

 These results are compiled by Clarke from a very large number 

 of analyses of river waters. The second column of the table 

 gives the mean heights in metres above sea level of the several 

 continents, as cited by Arrhenius. 3 



Of all the denudation results given in the table, those relating 

 to North America and to Europe are far the most reliable. 

 Indeed these may be described as highly reliable, being founded 

 on some hundreds or thousands of analyses, many of which have 

 been systematically pursued through every season of the year. 

 These show that Europe with a mean altitude of less than half 

 that of North America sheds to the ocean 25 per cent, more 



1 C. Schuchert, Bull. Geol. Soc. Am., vol. xx. 1910. 



2 See also Poulton, Address to Sect. D., Brit. Assoc. Rep. 1896. 



3 Lehrbuch der Kosmischen Physik, vol. i. p. 347. 



