GEOLOGICAL EVIDENCES. 299 



lower, being indispensable concomitants, then as now, ac- 

 cording to the field to be occupied and the function to be 

 performed. 



But while there are, have been, and will continue to be such 

 distinctions and inter-relations of life, geology has unfolded 

 a new phase, unknown to, and unthought of by, our ances- 

 tors. To the earlier botanists and zoologists the existing 

 aspect of life seemed complete, and only such diversities 

 were acknowledged as those produced by station and habi- 

 tat in the various latitudes of the world. Kow, however, 

 geology has revealed by proofs innumerable and unmistak- 

 able that myriads of forms have ceased to exist, that as we 

 go backward in time these forms become more simple or 

 less highly organised, and that a period is at last reached 

 when our planet was peopled only by the very lowest forms 

 of vegetable and animal existence. The establishment of 

 this ascent in time from lower to higher forms is one of the 

 noblest triumphs of geology a revelation that has invested 

 the scheme of life with new significance, and imparted to 

 its study a higher and more enduring interest. How broad 

 the Scheme of Life when living and extinct are conjoined ; 

 how marvellous the inter-relations that subsist between its 

 innumerable and varied parts ; and yet how ceaselessly the 

 whole has ever been passing onward into newer and higher 

 manifestations ! "What has been the order of this ascent ? 

 Has it been regular and progressive ? Is the higher form 

 linked on to the lower by characters that are invariable and 

 discoverable 1 and if so, what seems to be the law that has 

 regulated this progression and development 1 ? Such are 

 some of the questions suggested by the consideration of 

 this ascent of life ; and as Geology has revealed the fact, it 

 may be legitimately allowed to attempt an explanation. 



Assuming (and as yet we have no proof to the contrary) 

 that only the lowest or protozoan forms of life occur in the 



