168 THE POPULAR SCIENCE MONTHLY. 



enteenth century. The person who rendered this good service to pale- 

 ontology was Nicholas Steno, professor of anatomy in Florence, though 

 a Dane by birth. Collectors of fossils at that day were familiar with 

 certain bodies termed " glossopetrae," and speculation was rife as to 

 their nature. In the first half of the seventeenth century, Fabio Co- 

 lonna had tried to convince his colleagues of the famous Accademia 

 dei Lincei that the glossopetrae were merely fossil sharks' teeth, but his 

 arguments made no impression. Fifty years later Steno reopened the 

 question, and, by dissecting the head of a shark and pointing out the 

 very exact correspondence of its teeth with the glossopetrae, 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 fortunately oc- 

 curred to him to think out the whole subject of the interpretation of 

 fossils, and the result of his meditations was the publication, in 16G9, 

 of a little treatise with the very quaint title of " De Solido intra Soli- 

 dum naturaliter contento." The general course of Steno's argument 

 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 imbedded ; and the fundamental 

 problem of paleontology, stated generally, is this : " Given a body en- 

 dowed 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 production." * 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 reference to this particular case, that " bodies which 

 are altogether similar have been produced in the same way." f Hence, 

 since the glossopetrae are altogether similar to sharks' teeth, they must 

 have been produced by shark-like fishes ; and since many fossil shells 

 correspond, down to the minutest details of structure, with the shells 

 of existing marine or fresh- water animals, they must have been pro- 

 duced by similar animals ; and the like reasoning is applied by Steno 

 to the fossil bones of vertebrated animals, whether aquatic or terres- 

 trial. To the obvious objection that many fossils are not altogether 

 similar to their living analogues, differing in substance while agreeing 

 in form, or being mere hollows or imjDressions, the surfaces of which 

 are figured in the same way as those of animal or vegetable organisms, 

 Steno replies by pointing out the changes which take place in organic 

 remains imbedded in the earth, and how their solid substance may be 

 dissolved away entirely, or replaced by mineral matter, until nothing 

 is left of the original but a cast, an impression, or a mere trace of its 

 contours. The principles of investigation thus excellently stated and 

 illustrated by Steno in 16G9, are those which have, consciously or un- 



* " De Solido intra Solidum," p. 5. " Dato corporc certa figura prtedito et juxta leges 

 naturre producto, in ipso corpore argumenta iuvenire locum et modum productionis de- 

 tcgentia." 



f " Corpora sibi invicem omnino similia simili etiam modo producta sunt." 



