166 MEANING OP THE SYSTEM. 



palseontologically from each other in such a manner as to lend support 

 to the hypothesis of sudden and mighty revolutions and catastrophes 

 destroying the whole living world. We may rather assert with cer- 

 tainty, that the extinction of old species and the appearance of new 

 ones has not taken place at the same time at all points of the surface 

 of the earth, for many species extend from one formation into 

 another, and a number of organisms persist fi-om the tertiary period 

 to the present time, but little altered or even identical. Just as the 

 commencement of the recent epoch is hard to define, and cannot be 

 sharply separated from the diluvial period by the character either 

 of its deposits or of its fossils, so it is with the remoter periods of 

 the earth's history, which are founded, like periods of human history, 

 upon great and important occurrences, and yet are in direct con- 

 tinuity. 



Lyell has proved in a convincing way on geological grounds that 

 there, were not sudden revolutions extending over the whole surface 

 of the earth, but that changes took place slowly, and were confined * 

 to separate localities; in other words, that the past history of the 

 earth consists essentially of a gradual process of development, in which 

 the numerous forces which may be observed in action at the present 

 day have, by their long continued operation, had an enormous total 

 effect in transforming the earth's surface. 



The reason for the irregular development of strata and for the 

 limitations of formations is principally to be sought in the interrup- 

 tion of depositions, which, though widely distributed, were only of 

 local importance. Were it possible that a single basin of the sea 

 should have persisted during the whole period of sedimentary forma- 

 tion and under singularly favourable circumstances have formed new 

 deposits in persistent continuity, then we should find a progres- 

 sive series of strata interrupted by no gaps, which we should be 

 unable to classify according to formations. Such an ideal basin 

 would include only a single formation, in which we should find 

 representatives of all the other formations of the surface of the 

 earth. 



* " Every sedimentary formation was extended at the time of deposition over a 

 confined territory, confined on the one hand by the extent of the sea or fresh- 

 water basin, and on the other by the different conditions favourable to the depo- 

 sition inside the basin. At the same time, in other places entirely or at any 

 rate somewhat differently stratified formations (/./'., formations of the samea-e, 

 but of different composition) resulted. Thus marine, fresh-water, and swamp 

 formations have been deposited at the same time from different rocks and with 

 different fossils, while the land surface has remained free." Comp. B. Cotta, 

 '' Die Geologic der Gegenwart." 



