2l8 HEROES OF SCIENCE. 



captured off Leghorn in 1666, and especially dis- 

 cussed the mode of growth of the teeth of the 

 animal. At this time many fossils were picked up 

 and gathered out of layers or strata, which were 

 called by many curious names, and believed to be 

 anything but what they really were. They were 

 distinguished by Steno at once as shark's teeth, 

 and he insisted that sharks lived during the former 

 ages of the globe, and that they had become 

 entombed in the deposits which were then forming 

 a stratum or layer of earth, the result of deposition 

 in water, being the burial-ground of the time of its 

 collection or formation. 



Fossils were thus shown by Steno to be mineral- 

 ized or petrified organic remains, and he gave the 

 hint or method to future investigators, that the 

 example of the existing animals must be taken, in 

 order to learn the nature of those creatures whose 

 remains are more or less perfectly preserved in the 

 fossil condition. 



Following out this subject, Steno wrote on the 

 manner in which deposits accumulate, and accumu- 

 lated in past ages ; and he concluded that if we 

 found a deposit containing sea-salt and the remains 

 of marine animals, planks of ships etc., we should 

 believe that the sea had once been there, whether 

 the bed was exposed in consequence of the sea 

 having retired, or because the land had been 

 raised. He showed that although the lowest beds 

 deposited over any area, must conform to the shape 

 of the underlying rock, the tendency of all sediment 



