PREFACE. Xlll 



have, a uniform and infinite existence. With almost 

 equal force will these phenomena oppose that system 

 also, which considers the form and structure of the sur- 

 face of this planet, as resulting from a regularly recurring 

 series of similar mutations. 



The loss of whole species or genera, and the late cre- 

 ation of others, as is assumed in this work, are circum- 

 stances which strongly militate against both these hypo- 

 theses. It must, however, be acknowledged, that some 

 accurate inquirers have doubted whether a single species 

 has been thus lost. Bruguiere attempted to account for 

 this apparent extinction of several species of shell-fish, 

 by supposing that there are many genera, and even 

 families, which live constantly in the lowest depths of 

 the sea. These animals, which he termed Pelagian, 

 being entirely out of the reach of man, can only, he sup- 

 posed, become known to him by the mineralized remains 

 of those shells, which have been left in parts over which 

 former seas have flowed. Among these shells he places 

 the Ammonite, the Belemnite, and the Orthoceratite ; 

 but it is expected that it will be shown in the following 



