294 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1930 



The first rains, or perhaps more correctly the first condensation of 

 the atmospheric water, are of perfectly revolutionizing significance, 

 geologically, geochemically, and biologically. There would be rea- 

 sons to call the preaquatic time the primeval of the earth and the 

 time between the first condensation of water and the more general 

 appearance of determinable forms of animals the prehistoric time 

 of the earth and, finally, to refer the remaining younger parts to the 

 historic time of the earth. At any rate, the significance of the first 

 condensation of the water is not overestimated by this, that the time 

 of its appearance is made the boundary between two of the greatest 

 periods in the earth's history of evolution. 



As I already preliminarily stated, I only present a few reflections 

 here. I have hinted at the problems, and if I, with regard to the 

 geological ones, have also dared to make some suggestions as to their 

 solution, I have made them, fully conscious of the fact that the prob- 

 lems are still equally fresh and alluring and in man}'- points quite 

 unsolved. 



