28 PROGRESS OF PALEONTOLOGY n 



in favour of one or other of the last two hypo- 

 theses ; but it is much more profitable to try to 

 discover why they, who were really not one whit 

 less sensible persons than our excellent selvt >s, 

 should have been led to entertain views which 

 strike us as absurd. The belief in what is erro- 

 neously called spontaneous generation, that is to 

 say, in the development of living matter out of 

 mineral matter, apart from the agency of pre- 

 existing living matter, as an ordinary occurrence 

 at the present day which is still held by some of 

 us, was universally accepted as an obvious truth 

 by them. They could point to the arborescent 

 forms assumed by hoar-frost and by sundry 

 metallic minerals as evidence of the existence in 

 nature of a " plastic force " competent to enable 

 inorganic matter to assume the form of organised 

 bodies. Then, as every one who is familiar with 

 fossils knows, they present innumerable grada- 

 tions, from shells and bones which exactly re- 

 semble the recent objects, to masses of mere stone 

 which, however accurately they repeat the out- 

 ward form of the organic body, have nothing else 

 in common with it; and, thence, to mere traces 

 :nid faint impressions in the continuous substance 

 of the rock. What we now know to be the re- 

 sults of the chemical changes which take place in 

 the course of fossilisation, by which mineral is 

 substituted for organic substance, mi^ht, in the 

 absence of such knowledge, be fairly int i ]>K t.-d 



