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 owesmuch toextra-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 voleanic 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 
Paleozoic 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 knowa 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 havebeen less. 
The greater amount of carbon dioxide in the air dur- 
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