Chap. I. LIMITATION OF SPECIES IN TIME. 105 



Bohemia,' has come to the coudusioii that their species do not extend from one 

 formation to the other; D'Orbigny^ and Pictet^ have come to the same conclusion 

 for the fossil remains of all classes. It may -vvell bo said that, as fossil remains 

 are studied more carefully, in a zoiilogical point of view, the supposed identity of 

 species, in diflerent geological formations, vanishes gradually more and more ; so 

 that the limitation of species in time, already ascertained in a general way, by the 

 earlier investigations of their remains in successive geological formations, is circum- 

 scribed, step by step, within narrower, more definite, and also more equable periods. 

 Species are truly limited in time, as they are limited in space, upon the surface of 

 the globe. The facts do not exhibit a gradual disappearance of a limited number of 

 species, and an equally gradual introduction of an equally limited number of new 

 ones; Ijut, on the contrary, the simultaneous creation and the simultaneous destruc- 

 tion of entire founaj, and a coincidence between these changes in the organic world 

 and the great physical changes our earth has undergone. Yet it Avould be premature 

 to attempt to determine the extent of the geographical range of these changes, and 

 still more questionable to assert their synchronism upon the whole surface of the 

 globe, in the ocean and upon dry land. 



To form adequate ideas of the great physical changes the surface of our globe 

 has undergone, and the frequency of these modifications of the character of the 

 earth's surface, and of their coincidence with the changes observed among the organ- 

 iz.ed l)eings, it is nece&sary to study attentively the works of Elie de Beaumont.* 

 He, for the first time, attempted to determine the relative age of the difterent sys- 

 tems of mountains, and showed first, also, that the physical disturbances occasioned 

 Ijy their upheaval coincided with the successive disappearance of entire fauna?, and 

 the reappearance of new ones. In his earlier papers he recognized seven, then 

 twelve, afterwards fifteen such great convulsions of the globe, and now he has 

 traced more or less fully and conclusively the evidence that the number of these 

 disturbances has been at least sixty, perhaps one hundred. But while the genesis 

 and genealogy of our mountain systems were thus illustrated, palaeontologists, extend- 

 ing their comparisons between tlie fossils of different formations more carefully to 

 all the successive beds of each great era, have observed more and more marked 

 differences between them, and satisfied themselves that faunai also have been more 

 frequently renovated, than was formerly supposed; so that the general results of 



* Hauraxde, Sj-steinc silurien, etc., q. a. ; see, ■* Elie de Beaumont, Notice sur les systomes de 

 also, my IVronographics d'Ecliinoderines, (j. a., j>. 54. Montiigni's, Paris, 1852, 3 vols. 12mo. ; see, also, 



- D'OuiiiGNY, Paleontologie Fi-an^aisc, (|. a., ]). 95. Ikcii, (Leop. v.,) llebor die geognotischen Systeme 



* Pictet, Ti-aitc de Palcontologie, etc., (i- a., p. vcm Deutscliland, Lconhard's Tasclicnb., 1824, If., j). 

 96, note 1. 501. 



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