752 



SCIENCE. 



[N. S. Vol. XII. No. 307. 



cates like those which formed the primitive 

 crust. As a result of its action saline so- 

 lutions and chemical deposits would be 

 formed ; the latter, however, would proba- 

 bly be of no great thickness, for the time 

 occupied by the ocean in cooling to a tem- 

 perature not far removed from the present 

 would probably be included within a few 

 hundreds of years. 



THE STEATIFIED SERIES. 



The course of events now becomes some- 

 what obscure, but sooner or later the fa- 

 miliar processes of denudation and the 

 deposition started into activity, and have 

 continued acting uninterruptedly ever 

 since. The total maximum thickness of 

 the sedimentary deposits, so far as I can 

 discover, appears to amount to no less than 

 50 miles, made up as follows : 



Recent and Pleistocene 4,000. ..Man. 



Pliocene 5,000. ..Pithecanthropus. 



Miocene 9,000 



Oligocene 12,000 



Eocene 12,000...Entheria. 



Cretaceous 14,000 



Jurassic 8,000 



Trias 13,000.. .Mammals. 



Permian 12,000. ..Reptiles. 



Carboniferous 24,000. . .Amphibia. 



Devonian 22, 000... Fish. 



Silurian 15,000 



Ordovician 17,000 



Cambrian 16,000... In vertebrata. 



Keeweenawan 50,000 



Penokee 14,000 



Huronian 18,000 



Geologists, impressed with the tardy pace 

 at which sediments appear to be accumu- 

 lating at the present day, could not contem- 

 plate this colossal pile of strata without 

 feeling that it spoke of an almost inconceiv- 

 ably long lapse of time. They were led to 

 compare its duration with the distances 

 which intervene between the heavenly 

 bodies; but while some chose the distance 

 of the nearest lixed star as their unit, others 

 were content to measure the j'ears in terms 

 of miles from the sun. 



EVOLUTION OP OEGANISMS. 



The stratified rocks were eloquent of 

 time, and not to the geologist alone ; they 

 appealed with equal force to the biologist. 

 Accepting Darwin's explanation of the origin 

 of species, the present rate at which form 

 flows to form seemed so slow as almost to 

 amount to immutability. How vast then 

 must have been the period during which by 

 slow degrees and innumerable stages the 

 protozoon was transformed into the man I 

 And if we turn to the stratified column, 

 what do we find? Man, it is true, at the 

 summit, the oldest fossiliferous rocks 34 

 miles lower down, and the fossils they con- 

 tain already representing most of the great 

 classes of the Invertebrata, including Crus- 

 tacea and Worms. Thus the evolution of 

 the Vertebrata alone is known to have oc- 

 cupied a period represented by a thickness 

 of 34 miles of sediment. How much greater, 

 then, must have been the interval required 

 for the elaboration of the whole organic 

 world ! The human mind, dwelling on 

 such considerations as these, seems at times 

 to have been affected by a sur- excitation of 

 the imagination, and a consequent paraly- 

 sis of the understanding, which led to a re- 

 fusal to measure geological time by years 

 at all, or to reckon by anything less than 

 ' eternities.' 



GEOLOGIC PERIODS OF TIME. 



After the admirable address of your Pres- 

 ident last year it might be thought needless 

 for me to again enter into a consideration 

 of this subject ; it has been said, however, 

 that the question of geological time is like 

 the Djin in Arabian tales, and will irre- 

 pressibly come up again for discussion, 

 however often it is disposed of. For my 

 part I do not regard the question so de- 

 spond ingly, but rather hope that by per- 

 severing effort we may succeed in discover- 

 ing the talisman by which we may compel 

 the unwilling Pjin into our service. How 



