THE EUROPEAN SEAS. 



249 



which have been very fully represented in former 

 periods, are very sparingly so now. 



To such as are acquainted with the general out- 

 line of the earth's natural history, past and present 

 — who know that our European tribes of animals 

 and plants have not through all time had their 

 being on our area — that before them have been 

 numerous other assemblages in succession, and 

 wholly different — many questions must have sug- 

 gested themselves as to the manner in which the 

 change from one fauna to another was brought 

 about, how old forms disappeared, whence new 

 forms came in. 



Our knowledge of the remote past, with all its 

 changes, is mostly derived from the accumulations 

 of old seas, lakes, and estuaries ; and if any satis- 

 factory answers are ever to be given to the fore- 

 going queries, they must be derived from a close 

 and careful study of all the influences which de- 

 termine the distribution and development of life 

 now, within such-like areas. The inquiry is alto- 

 gether distinct from those difficult questions, so 

 often put — what is a species'? and how do new 

 species come into existence 1 and it resolves itself 

 into this — where and what is that marine fauna in 

 which we can first recognise the existing forms of 

 our European seas? 



Before entering on this inquiry, the meaning of 

 the expression " a marine fauna " must be clearly 

 defined ; to say that it is such an assemblage as 



