12 A Century of Science 



back to enormously remote periods of time, began 

 to teach that the forces at work have all along 

 been the same forces that are operative now. Of 

 course, in that early stage when the earth's crust 

 was in process of formation, when the temperature 

 was excessively high, there were phenomena here 

 such as can no longer be witnessed, but for which 

 we must look to big planets like Jupiter ; in that 

 intensely hot atmosphere violent disturbances oc- 

 cur, and chemical elements are dissociated which we 

 are accustomed to find in close combination here. 

 But ever since our earth cooled to a point at which 

 its solid crust acquired stability, since the earliest 

 mollusks and vertebrates began to swim in the 

 seas and worms to crawl in the damp ground, if at 

 almost any time we could have come here on a 

 visit, we should doubtless have found things going 

 on at measured pace very much as at present, 

 here and there earthquake and avalanche, fire and 

 flood, but generally rain falling, sunshine quick- 

 ening, herbage sprouting, creatures of some sort 

 browsing, all as quiet and peaceful as a daisied 

 field in June, without the slightest visible presage 

 of the continuous series of minute secular changes 

 that were gradually to transform a Carboniferous 

 world into what was by and by to be a Jurassic 

 world, and that again into what was after a while 



