THROUGH THE GEOLOGIST'S EYES 



the tides and the ocean-currents, which were prob- 

 ably much more powerful in early than in late geo- 

 logic times, and to submarine mineral springs and 

 volcanic eruptions of ashes and mud, admits of little 

 doubt. That it owes much to extra-terrestrial sources 

 — to meteorites and meteoric dust — also admits 

 of little doubt. 



It seems reasonable that earlier in the history of 

 the evolution of our solar system there should have 

 been much more meteoric matter drifting through 

 the interplanetary spaces than' during the later ages, 

 and that a large amount of this matter should have 

 found its way to the earth, in the form either of solids 

 or of gases. Probably much more material has been 

 contributed by volcanic eruptions than there is any 

 evidence of apparent. The amount of mineral mat- 

 ter held in solution by the primordial seas must have 

 been enormous. The amount of rock laid down in 

 Palaeozoic times is estimated at fifty thousand feet, 

 and of this thirteen thousand feet were limestone; 

 while the amount laid down in Mesozoic times, 

 for aught we know a period quite as long, amounts to 

 eight thousand feet, indicating, it seems to me, that 

 the deposition of sediment went on much more rap- 

 idly in early geologic times. We are nearer the begin- 

 ning of things. All chemical processes in the earth's 

 crust were probably more rapid. Doubtless the rain- 

 fall was more, but the land areas must have been less. 

 The greater amount of carbon dioxide in the air dur^ 



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