EVOLUTION OF ORGANISMS 15 



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 ! And if we turn to the 

 stratified column, what do w r e find? Man, it is true, at 

 the summit, the oldest fossiliferous rocks thirty-four miles 

 lower dow T n, and the fossils they contain already repre- 

 senting 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 by a thickness of thirty-four miles of sedi- 

 ment. 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 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." 



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 despondingly, 

 but rather hope 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 ! 



