82 GEOLOGICAL BIOLOGY. 



and the relations which their specific forms bear to the place 

 they occupy in the geological scale, which indicate a definite- 

 ness in the order of their succession, quite independent of the 

 evidence furnished by the stratigraphic succession of the rocks 

 themselves ; and it is this testimony of the fossils, pure and 

 simple, as mere physical forms, upon or in the rocks, that con- 

 firms and helps to complete the chronological scale indicated 

 by the successive geological systems. 



Pictet* announced a number of propositions setting forth 

 the more prominent of the laws of occurrence of fossils and 

 their relations to time and place. In the " Handbuch der 

 Palseontologie " Zittel f has condensed and culled them so 

 carefully that we there have concisely formulated in a few 

 sentences the chief facts regarding their occurrence. 



They are as follows: (i) All stratified sedimentary rocks 

 (with the exception of metamorphic rocks) enclose, more or 

 less richly, fossils, and thus prove that the earth, for an im- 

 measurable length of time before the appearance of man, was 

 inhabited by organisms. 



(2) The fossils of the oldest and deepest strata represent 

 extinct species, and for the most part extinct genera ; only 

 in the more recent strata are found forms which are identical 

 with those now living. The deeper down we penetrate in the 

 series of strata the more divergent are the fossils from the 

 forms now living; and, on the contrary, rising from the earli- 

 est to the more recent formations there is a continuously 

 increasing resemblance to the present creation. 



(3) The different fossil faunas and floras follow each other 

 the world over in the same regular sequence ; the formations 

 stratigraphically nearer to each other contain the most similar 

 fossils, and those most separated in age present the greater 

 differences. 



(4) Constant change characterizes the evolution of the 

 organic creation. Species of one geological formation are 

 either completely or partly replaced by other species in the 

 next superimposed strata. 



* Pictet, Frangois Jules, " Traite de paleontologie : ou, hist. nat. des ani- 

 maux fossiles, etc. ' 1853-57. 



f Zittel, " Handbuch der Palseontologie," vol. i. pp. 17, 18. 



