THROUGHOUT THE WORLD. 331 



still be manifest, and the several formations could be easily 

 correlated. 



These observations, however, relate to the marine inhab- 

 itants of the world: we have not sufficient data to judge 

 whether the productions of the land and of fresh water at 

 distant points change in the same parallel manner. We 

 may doubt whether they have thus changed : if the Mega- 

 therium, Mylodon, Macrauchenia, and Toxodon had been 

 brought to Europe from La Plata, without any information 

 in regard to their geological position, no one would have 

 suspected that they had co-existed with sea-shells all still 

 living; but as these anomalous monsters co-existed with 

 the Mastodon and Horse, it might at least have been in- 

 ferred that they had lived during one of the later tertiary 

 stages. 



When the marine forms of life are spoken of as having 

 changed simultaneously throughout the world, it must not 

 be supposed that this expression relates to the same year, 

 or to the same century, or even that it has a very strict 

 geological sense ; for if all the marine animals now living in 

 Europe, and all those that lived in Europe during the pleis- 

 tocene period (a very remote period as measured by years, 

 including the whole glacial epoch) were compared with those 

 now existing in South America or in Australia, the most skil- 

 ful naturalist would hardly be able to say whether the pres- 

 ent or the pleistocene inhabitants of Europe resembled most 

 closely those of the southern hemisphere. So, again, several 

 highly competent observers maintain that the existing pro- 

 ductions 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 European beds. Neverthe- 

 less, looking to a remotely future epoch, there can be little 

 doubt that all the more modern marine formations, namely, 

 the upper pliocene, the pleistocene, and strictly 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 

 underlying deposits, would be correctly ranked as simulta- 

 neous in a geological sense. 



The fact of the forms of life changing simultaneously in 

 the above large sense, at distant parts of the worlcl, has 



