WORLD-MAKING 23 



astonished that fierce geological battles have raged over the 

 old crystalline rocks. By some geologists they are almost 

 entirely explained away, or referred to igneous action, or to the 

 alteration of ordinary sediments. Under the treatment of 

 another school they grow to great series of Pre-Cambrian 

 rocks, constituting vast systems of formations, distinguishable 

 from each other chiefly by differences of mineral character. 

 Facts and fossils are daily being discovered, by which these 

 disputes will ultimately be settled. 



After the solitary appearance of Eozoon in the Laurentian, 

 and of a few uncertain forms in the Huronian, we find our- 

 selves, in the Cambrian, in the presence of a nearly complete 

 invertebrate fauna of protozoa, polyps, echinoderms, mollusks 

 and Crustacea, and this not confined to one locality merely, 

 but apparently extended simultaneously throughout the ocean, 

 over the whole world. This sudden incoming of animal life, 

 along with the subsequent introduction of successive groups of 

 invertebrates, and finally of vertebrate animals, furnishes one of 

 the greatest unsolved problems of geology, which geologists 

 were wont to settle by the supposition of successive creations. 

 In the sequel I shall endeavour to set forth the facts as to this 

 succession, and the general principles involved in it, and to 

 show the insufficiency of certain theories of evolution suggested 

 by biologists to give any substantial aid to the geologist in 

 these questions. At present I propose merely to notice some 

 of the general principles which should guide us in studying the 

 development of life in geological time, and the causes which 

 have baffled so many attempts to throw light on this obscure 

 portion of our unsolved problems. 



It has been urged on the side ot rational evolution — and' 

 there are both rational and irrational forms of this many-sided 

 doctrine — that this hypothesis does not profess to give an 

 explanation of the absolute origin of life on our planet, or even 

 of the original organization of a single cell, or of a simple mass 



