220 GEOLOGICAL TIME 



palaeontological evidence in favour of the general 

 quietude of the geological processes in the past. The 

 conclusions drawn from the nature and arrangement 

 of the sediments are corroborated and much extended 

 by the structure and manner of entombment of the 

 enclosed organic remains. From the time of the very 

 earliest fossiliferous formations there is nothing to 

 show that either plants or animals have had to con- 

 tend with physical conditions of environment different, 

 on the whole, from those in which their successors 

 now live. The oldest trees, so far as regards their 

 outer form and internal structure, betoken an atmo- 

 sphere neither more tempestuous nor obviously more 

 impure than that of to-day. The earliest corals, 

 sponges, crustaceans, mollusks, and arachnids were not 

 more stoutly constructed than those of later times, 

 and they are found grouped together among the rocks 

 as they lived and died, with no apparent indication 

 that any violent commotion of the elements tried 

 their strength when living or swept away their re- 

 mains when dead. 



But, undoubtedly, most impressive of all the palae- 

 ontological data is the testimony borne by the grand 

 succession of organic remains among the stratified 

 rocks as to the vast duration of time required for their 

 evolution. Professor Poulton has treated this branch 

 of the subject with great fulness and ability (p. 216). 

 We do not know the present average rates of organic 

 variation, but all the available evidence goes to indicate 

 their extreme slowness. They may conceivably have 

 been more rapid in the past, or they may have been 

 liable to fluctuations according to vicissitudes of 



