ORIGIN OF THE PROBLEM 5 



even on the mountains. Endeavours were made to 

 explain this in very varied ways, either by acceptance 

 of oceanic floods which carried the sea animals inland, 

 or it was disputed that they were really the remains 

 of pre-existent life. 



To this end a peculiar force in stone was conceived 

 nisus formativus, or petrif active force which, with or 

 without the assistance of the stars, imitated organic 

 forms from inorganic materials. 



This opinion, in the sixteenth and seventeenth 

 centuries, was the ruling one despite the better know- 

 ledge of some eminent men. 



Leonardo da Vinci, for instance, would have nothing 

 to do with such enigmatical working of the constellations. 



Since, however, it was considered that the earth 

 and its organisms had been created as they then were, 

 the nisus formativus appeared to be the more accept- 

 able explanation. Consequently the ' petrifactions ' 

 were not at all regarded as the remains of organisms 

 which at one time had really lived ; and of a connec- 

 tion with the living animals and plants of to-day no 

 one then thought. The opinions of the time are shown, 

 for instance, in A. Kircher's ' Mundus subterraneus ' 

 (Figs. 1-4). i 



Since, however, the number of such ' figure stones '. 

 discovered constantly increased, grave doubts began 

 to arise against the nisus formativus theory, especially 



1 II, Amstelodami 1665, c. 9. Kircher also stated that many of these 

 lusus naturae might have originated through hollow spaces in the earth 

 becoming filled with mud. 



