292 GEOLOGY. 



plex and active an organism as that of the trilobite implies an excellent 

 development of the nervous system. It is not safe to attempt to 

 say how far this admirable mechanism was directed by conscious intelli- 

 gence, as distinguished from what we choose to call automatic or instinc- 

 tive action, but there is food for thought in placing ourselves face to 

 face with the alternative of either assigning these fine organisms and 

 their complex activities to unconscious automatism, or else of recogniz- 

 ing in them the early stages of conscious psychology. Whether our 

 interpretations be wholly correct or not, it is better to give a passing 

 thought to these higher problems than to ignore one of the most vital 

 phases of life-evolution. 



Ecological adaptations. — A study of the distribution of the Cam- 

 brian fossils gives indications that then, as ever since, there was an 

 adaptation of life to its immediate physical environment. The life 

 appears to have varied with the nature of the bottom, with the depth 

 of the water, and with other marine conditions, much as it does to-day. 

 There were mud-bottom faunas, sand-bottom faunas, and like adapta- 

 tions. There seem to have been zones of shore life (littoral), of off- 

 shore life (photobathic), and of deep-sea life (pelagic and abysmal), 

 although the evidence of the last is scant. It is important to recog- 

 nize these variations in the comparison and correlation of faunas, for 

 considerable differences may occur among faunas which were strictly 

 contemporaneous. Except in the case of floating forms, that are 

 relatively indifferent to the bottom, it is usually possible to judge of 

 the nature of the conditions under which the animals lived from the 

 mature of the sediments in which the fossils are imbedded. 



Zoological provinces. — The assemblages of the life of the period 

 seem to have varied in a broader way, giving rise to zoological provinces. 

 The leading agents in developing these provinces were probably barriers 

 that isolated certain portions of the sea from other portions. The 

 isolation was not complete in most cases, but reached such a degree 

 of separation as to cause the life of each area to develop along its own 

 lines, in more or less independence of the evolution of other regions. 

 The leading principles involved have been set forth in Volume I, pp. 663- 

 672, particularly in that portion which relates to provincial and cos- 

 mopolitan evolution, pp. 668-672. 



The early faunas of the Cambrian were somewhat provincial in 

 nature, though the provinces appear to have been large. Toward 



