GEOLOGICAL SUCCESSION OF ORGANIC BEINGS »S 



tions of the United States are more closely related to those which 

 lived in Europe during certain late tertiary stages, than to the 

 present inhabitants of Europe; and if this be so, it is evident that 

 fossiliferous beds now deposited on the shores of North America 

 would hereafter be liable to be classed with somewhat older Eu- 

 ropean beds. Nevertheless, looking to a remotely future epoch, 

 there can be little doubt that all the more modem marine forma- 

 tions, namely, the upper pliocene, the pleistocene, and strictlj 

 modern beds of Europe, North and South America, and Australia, 

 from containing fossil remains in some degree allied, and from 

 not including those forms which are found only in the older under- 

 lying deposits, would be correctly ranked as simultaneous in a 

 geological sense. 



The fact of the forms of life changing simultaneously in the 

 above large sense, at distant parts of the world, has greatly struck 

 those admirable observers, MM. de Verneuil and d'Archiac. After 

 referring to the parallelism of the palaeozoic forms of life in various 

 parts of Europe, they add: "If, struck by this strange sequence, 

 we turn our attention to North America, and there discover a 

 series of analogous phenomena, it will appear certain that all 

 these modifications of species, their extinction, and the introduc- 

 tion of new ones, cannot be owing to mere changes in marine cur- 

 rents or other causes more or less local and temporary, but depend 

 on general laws which govern the whole animal kingdom." M. 

 Barrande has made forcible remarks to precisely the same effect. 

 It is, indeed, quite futile to look to changes of currents, climate^ 

 or other physical conditions, as the cause of these great mutations 

 in the forms of life throughout the world, under the most differ- 

 ent climates. We must, as Barrande has remarked, look to some 

 special law. We shall see this more clearly when we treat of the 

 present distribution of organic beings, and find how slight is the 

 relation between the physical conditions of various countries and 

 the nature of their inhabitants. 



This great fact of the parallel succession of the forms of life 

 throughout the world, is explicable on the theory of natural selec- 

 tion. New species are formed by having some advantage over older 

 forms; and the forms which are already dominant, or have some 

 advantage over the other forms in their own country, give birth to 

 the greatest number of new varieties or incipient species. We have 

 distinct evidence on this head, in the plants which are dominant, 

 that is, which are commonest and most widely diffused, producing 

 the greatest number of new varieties. It is also natural that the 

 dominant, varying and far-spreading species, which have already 



