FIRST CRITICAL PERIOD 5 



not that physicists occasionally invade our borders, but 

 that they do not visit us oftener and make closer 

 acquaintance with us. 



If I am bold enough to assert that cosmogony is no 

 longer alien to geology, I may proceed further, and, 

 taking advantage of my temerity, pass on to speak of 

 things once not permitted to us. I propose, therefore, to 

 offer some short account of the early stages in the history 

 of the earth. Into its nebular origin we need not inquire 

 that is a subject for astronomers. We are content to 

 accept the infant earth from their hands as a molten 

 globe ready made, its birth from a gaseous nebula duly 

 certified. If we ask, as a matter of curiosity, what was 

 the origin of the nebula, I fear even astronomers cannot 

 tell us. There is an hypothesis which refers it to the 

 clashing of meteorites, but in the form in which this 

 is usually presented it does not help us much. Such 

 meteorites as have been observed to penetrate our atmo- 

 sphere and to fall on to the surface of the earth prove on 

 examination to have had an eventful history of their own 

 of which not the least important chapter was a passage 

 through a molten state ; they would thus appear to be 

 the products rather than the progenitors of a nebula. 



We commence our history, then, with a rapidly rotating 

 molten planet, not impossibly already solidified about the 

 centre and surrounded by an atmosphere of great depth, 

 the larger part of which was contributed by the water of 

 our present oceans, then existing in a state of gas. This 

 atmosphere, which exerted a pressure of something like 

 5,000 Ib. to the square inch, must have played a very 

 important part in the evolution of our planet. The 

 molten exterior absorbed it to an extent which depended 

 on the pressure, and may some day be learnt from 

 experiment. Under the influence of the rapid rotation 

 of the earth the atmosphere would be much deeper in the 



