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~ Snor. TJ CLIMATES OF THE PAST. 21 
much more frequent and larger, and accordingly the rate of oceanic 
denudation much accelerated. The more rapid alternation of day 
and night’* would probably lead to more sudden and violent storms, 
_ and the increased rotation of the earth would augment the violence 
_ of the trade-winds, which in their turn would affect oceanic 
eurrents.”* As above stated, no facts yet revealed by the geological 
record compel the admission of more violent superficial action in 
former times than now. But though the facts do not of themselves 
lead to such an admission, itis proper to inquire whether any of them 
are hostile to it. It will be shown in Book VI. that even as far back 
as early Paleozoic times, that is, as far into the past as the history 
of organised life can be traced, sedimentation took place very much 
as it does now. Sheets of fine mud and silt were pitted with rain- 
drops, ribbed with ripple-marks, and furrowed by crawling worms 
exactly as they now are on the shores of any modernestuary. These 
surfaces were quietly buried under succeeding sediment of a similar 
kind, and this for hundreds and thousands of feet. Nothing 
indicates violence; all the evidence favours tranquil deposit. If, 
therefore, Mr. Darwin’s hypothesis be accepted, we must conclude 
either that it does not necessarily involve such violent superficial 
operations as he supposes, or that even the oldest sedimentary 
formations do not date back to a time when the influence of increased 
rotation could make itself evident in sedimentation, that is to say, 
on Mr. Darwin’s hypothesis, the most ancient fossiliferous rocks 
cannot be nearly as much as 97,000,000 years old. 
§ 8. Climate in its Geological Relations.—In subsequent parts 
of this volume the data will be given from which we learn that the 
climates of the earth have formerly been considerably different from 
those which at present prevail. A consideration of the history 
of the solar system would of itself suggest the inference that 
on the whole the climates of early geological periods must have 
been warmer. ‘The sun’s heat was greater, probably the amount of 
it received by the earth was likewise greater, while there would be 
for some time a sensible influenze of the planet’s own internal heat 
upon the general temperature of the whole globe. Although 
arguments based upon the probable climatal necessities of extinct 
species and genera of plants and animals must be used with extreme 
caution, it may be asserted with some confidence that from the vast 
areas over which many Paleozoic molluses have been traced alike in 
the eastern and the western hemispheres, the climates of the globe 
in Paleeozoic time were probably much more uniform than they now 
a According to his calculation, the year 57,000,000 of years ago contained 1300 days 
instead of 365. 2 Op. ctt. p. 532. 
_ 3 As Professor Tait has suggested, we can conceive that the former greater heat of 
the sun may have raised such vast clouds of abscrbing vapour round that luminary as to 
prevent the effective amount of radiation of heat to the earth’s surface from being greater 
than at present; while on the other hand, a similar supposition may be made with 
reference to the greater amount of vapour which increased solar radiation would raise 
to be condensed in the earth’s atmosphere. Recent Advances in Physical Science, 1876, 
fp. 174. 
