THE EUROPEAN SEAS. 



271 



nature of the process of local change may have 

 been the same, and that it does not follow that 

 forms have been newly created because they appear 

 to us to make their first appearance at some given 

 stage of a geological formation. 



The single instance of the occurrence of a Lusi- 

 tanian form, such as Lutraria rugosa, in our seas at 

 an early stage of our fauna, its subsequent complete 

 extinction in all seas, within a distance of four hun- 

 dred miles in latitude, admits of useful application 

 by the f> alseontologist. This, though a striking, is 

 by no means a solitary instance. If the history of 

 every component member of the marine fauna of 

 our European seas was written in detail, from its 

 earliest appearance downwards, they would all agree 

 in respect of these apparent migratory movements 

 in time, differing only in degree. 



From the copious fauna which now tenants the 

 Mediterranean waters, a series of changes may be 

 traced, through older sea-beds of the same area, far 

 back into bygone ages. Nowhere do we find better 

 illustration than here of the nature of the change 

 which a fauna may undergo in time : the evidence 

 is consecutive. It is possible, however, that the 

 Mediterranean series, recent and fossil, may be im- 

 perfect, and that the earliest periods of our European 

 marine fauna are not represented there. A com- 

 parison of the contents of the older Italian deposits, 

 and their equivalents, containing the remains of 

 existing Atlantic species of Testacea, with those of 



