CAUSE OF THE SUCCESSION OF LIFE IN TIME. 445 



produce fever. A ferruginous spring entering a river may kill the 

 fish for miles. 1 Such and such-like conditions may account for the 

 appearances of sudden mortality which are familiar to the geologist, 

 but the extinction of species even locally is a phenomenon of another 

 order, and is in most cases to be attributed to the upheaval and 

 depression of land. 



PalaBontological Laws. Pictet summarised palaeontological belief 

 in the following laws : i. All species have had a limited geological 

 duration. 2. The contemporary species of a geological fauna in any 

 one locality in most cases appeared simultaneously, and disappeared in 

 the same manner. 3. The differences between living and extinct 

 faunas are in proportion to the geological antiquity of the extinct 

 fauna. 4. The diversity of animal organisation has increased with 

 the duration of geological time. 5. The highest types of life have a 

 comparatively recent origin. 6. The order of appearance on the earth 

 of the different types of life often recalls the phases of embryological 

 development. 7. The existence of a type upon the earth is uninter- 

 rupted from its first appearance to its extinction. 8. The ancient 

 distribution of life shows that the distribution of temperature has 

 changed. 9. The geographical distribution of species found in the 

 strata was more extended than the range of species of existing faunas. 

 10. Fossil animals were constructed on the same plan as existing 

 animals, and their lives manifested the same physiological functions. 2 



Succession of Life in Time. Just as the earth's surface at the 

 present day is inhabited by groups of animals and plants, as distinct 

 from each other as are the faunas of past ages of geological time, so 

 every era, the earth being divided up into masses of land and 

 water, must always have had its life characterised by differences in 

 the generic groups of species in different regions, which amounted to 

 provinces, comparable to those which have been established upon the 

 distribution of living animals and plants. Hence the fauna or flora 

 of a geological formation is nothing but a natural history life pro- 

 vince, which has become preserved in sediments, which enclosed 

 organic remains in the positions in which they once lived, and are now 

 found. And every life province, whether on land or in the sea, 

 is only a geological fauna or flora which is now becoming fossilised. 

 Formerly there was a belief that the physical conditions which caused 

 the deposition of a new mineral sediment affected the whole surface 

 of the earth, or were of the nature of " catastrophes," and that many 

 successive creations replaced the life which was supposed to have been 

 periodically exterminated. Such ideas of catastrophe and creation 

 find no support in the observations which geologists have accumu- 

 lated. On the other hand, Lyell and Darwin, and the uniformitarian 

 school, by supposing that life, when it was once placed upon the 

 earth, had become gradually and successively modified from age to 

 age, appealed to " breaks in time " and the " imperfection of the 

 geological record," as means of accounting for differences which were 



1 Geol. Mag., vol. ix. p. 533. 



2 "Traite de Paisontologie," tome i. 1853. 



