30 PROGRESS OF PALAEONTOLOGY n 



the famous Accademia del Lincei that the glosso- 

 petrss were merely fossil sharks' teeth, but his 

 arguments made no impression. Fifty years later, 

 Steno re-opened the question, and, by dissecting 

 the head of a shark and pointing out the very 

 exact correspondence of its teeth with the glosso- 

 petras, left no rational doubt as to the origin of 

 the latter. Thus far, the work of Steno went 

 little further than that of Colonna, but it for- 

 tunately occurred to him to think out the whole 

 subject of the interpretation of fossils, and the 

 result of his meditations was the publication, 

 in 1669, of a little treatise with the very quaint 

 title of " De Solido intra Solidum naturaliter 

 contento." The general course of Steno's argu- 

 ment may be stated in a few words. Fossils are 

 solid bodies which, by some natural process, have 

 come to be contained within other solid bodies, 

 namely, the rocks in which they are embedded ; 

 and the fundamental problem of palasontology, 

 stated generally, is this : " Given a body endowed 

 with a certain shape and produced in accordance 

 with natural laws, to find in that body itself the 

 evidence of the place and manner of its pro- 

 duction." ] The only way of solving this problem 

 is by the application of the axiom that " like 

 effects imply like causes/' or as Steno puts it, in 



1 De Solido intra Solidum, p. 5. "Dato corpore certa figura 

 prsedito et juxta leges naturse producto, in ipso corpora 

 a%umenta in venire locum et modum productionis detegentia." 



