X907.] AND CONTRACTION OF THE EARTH. 221 



rate of the elevation of the Andes, taken at only one tenth of an inch 

 a year, or ten inches in a century, seem to show that the age of these 

 mighty mountains need not much exceed three million years. In the 

 case of the mountains west of the Rockies a numerical estimate is not 

 quite so easy, but it is doubtful if anything authorizes an estimate 

 exceeding five million years. In this immense period the whole 

 country west of Laramie may have been raised from the sea ; in fact 

 this is indicated by the abundant fossils of Saurians in the beds of 

 Wyoming, as well as by the numerous parallel ranges of mountains 

 in Nevada and California, showing the successive recessions of the 

 sea. One is led therefore to think that after all our consolidated 

 globe may not have an age exceeding eight or ten million years. In 

 comparison with the brevity of human history such periods are almost 

 infinite; and so little is known of the rates of variation of organic 

 species under the unknown conditions of the past, that we may well 

 hesitate before assuming longer periods for the life of our encrusted 

 planet. 



In contemplating this result we are again confronted with the 

 question of the cosmical significance of radium. Several years ago 

 when the enthusiasm over the radium discoveries was at its height 

 there were those who admitted a terrestrial history of a thousand 

 million years (cf. Professor Sir G. H. Darwin's presidential address 

 to the British Association at Capetown, 1905). But mysterious as 

 radium still remains, it is doubtful if such a view is generally held to- 

 day. It is a remarkable fact that the more we study radium, the 

 less we seem to really understand the part it plays in cosmical proc- 

 esses. So far at least there is no proof that it exerts any sensible 

 influence, except possibly in chemical transformations. 

 § 12. Some of the Results of the Researches on Radium. 



In spite of the great labor bestowed upon the study of radium by 

 many devoted and enthusiastic investigators, it can hardly be said 

 that we have up to this time any conclusive results as to the cosmical 

 significance of this very wonderful element. The theories of radium 

 disintegration are well known, but not universally accepted. Lord 

 Kelvin is one of those who still ascribe the Sun's heat to the potential 

 energy of the mutual gravitation of its own matter; and he denies 

 that radium plays any appreciable part in solar activity. 



