Transactions of section c. 



7i7 



tlie sedimentary deposits, so far as 

 than 50 miles, made up as follows :— 



I can discover, appears to amount to no less 



Geologists, impressed witii the tardj^ pace at which sediments appear to be 

 accumulating at the present day, could not contemplate this colossal pile of strata 

 ■without feeling that it spolie of an almost inconceivably long lapse of time. They 

 were led to compare its duration witli tlie distances which intervene between the 

 heavenly bodies ; but while some chose the distance of the nearest fixed star as 

 their unit, others were content to measure the years in terms of miles from the sun. 



Evolution of Organisms. 



The stratified rocks were eloquent of time, and not to tlie geologist alone, 

 they appealed with equal force to tlie 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. IIow vast then must have been the 

 period during which by slow degrees and innumerable stages the protozoon was 

 transformed into the man ! 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 contain already representing most of the great 

 classes of the Invertebrata, including Crustacea and Worms. Thus the evolution 

 of the Vertebrata alone is known to have occupied a period represented hy 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 liave been 

 affected by a sur-excitation of the imagination, and a consequent paralysis of the 

 understanding, which led to a refusal 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 President 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 irrepressibly come up again for discussion, however often it is 

 disposed of For my part I do not regard the question so despondinglv, but rather 

 liope that by persevering effort we may succeed in discovering the talisman by 

 which we may compel the unwilling Djin into our service. How immeasurable 

 would be the advance of our science could we but bring the chief events which 

 it records into some relation with a standard of time ! 



Before proceeding to the discussion of estimates of time drawn from a ftudy 

 of stratified rocks let us first consider those which have been already suo-o-ested 

 by other dati. These are as follows: — il) Time which has elapsed since the 



