during the Formation of the Crust of the Earth, 89 



II. Results of investigations regarding the gradation or simulta- 

 neousness of the appearance and disappearance of organized 

 beings. 



The results at which we have arrived, with regard to the gra- 

 dual or simultaneous extinction of all the organisms of a single 

 epoch, may be summed up in the following manner : — 



1. The creation of new species and the disappearance of older 

 types went on continuously, with the exception of slight oscil- 

 lations, without being restricted to certain periods of creation, 

 although it is easy to imagine that certain geological events may 

 have, here and there, induced the simultaneous extinction of a 

 larger or smaller number of species. 



3. The duration of existence has been very variable, according 

 to the species. Certain specific types have endured 2, 3, 4, or 5 

 times as long as others, so that some even existed only during a 

 small fraction of the time necessary for the production of a for- 

 mation in the geological sense of the word, whilst others survived 

 the deposition of two or three formations, or even more. These 

 phsenomena might take place only at a certain point of the sur- 

 face of the globe, and not present themselves elsewhere. 



3. There are, consequently, no definite formations in the 

 palseolithic sense of the word, no definite creations, no successive 

 and well-marked floras or faunas, any more than there exists 

 any formation which simultaneously maintains the sameminera- 

 logical characters, the same thickness, and the same lithological 

 and palseontological characters in all parts of the world. 



4. A geological formation, or a geological flora or fauna, is 

 the totality of the sedimentary strata which have been formed 

 upon the whole earth during a certain space of time, or the 

 totality of the animals and plants which have lived during that 

 space of time. It is of little consequence here, whether the 

 lithological character, the thickness, and the limits of demar- 

 cation of these strata have been uniform over all the surface of 

 the globe, or have varied in difi*erent places, assuming here one 

 aspect, there another; it is of little consequence whether the 

 various species of organisms belonging to this epoch may have 

 lived from its commencement to its termination, only endured 

 for a portion of this time, or passed the limits assigned to this 

 formation. 



5. When the deposition of identical strata, according with an 

 identical and constant state of the sea, continued longer in one 

 country than in another, the population of this sea and the 

 organic remains of this population might exist there longer 

 without undergoing modification. 



6. When an identical state of the sea reappeared during the 



