of the White Chalk of the Paris Basin. 391 



ill the environs of Sienna in Italy, they often constitute one- 

 sixth of the fossil mass; they are also extensively distributed 

 in the Crug of England* and of Belgium. So much in refer- 

 ence to what has existed; let us now throw a glance upon 

 that which exists. 



We are in the present day acquainted with Foraminifers 

 from every region of the sea, and we know that they exist in 

 extent from the equator to the frozen jiortions of continents. 

 If we judge of the important part they play by their numbers 

 in certain quarters, it will be impossible to doubt that their 

 remains form the greater part of the banks of sand which im- 

 pede navigation, obstruct gulfs and straits, fill up ports, and 

 form with corals those isles which are daily rising in warm 

 regions from the bosom of the ocean. 



Thus these minute shells, which, anterior to our epoch, 

 have assisted in leveling basins of immense extent, and in 

 forming mountains, are now still ccmstantly changing the 

 depth of coasts and modifying the bottom. This view of their 

 agency in nature is doubtless sufficient to prove the import- 

 ance which attaches to their study. 



We will add, that the comparative study of the fossil Fora- 

 minifers of all beds has proved to us a fact important to 

 geology, namely, that each bed has its characteristic species, 

 which serve to distinguish it, let the circumstances be what 

 they may; and as these minute shells are infinitely more com- 

 mon than those ofMollusks, the knowledge to be derived 

 from them is so much the more certain, and becomes extremely 

 interesting. 



Another fact no less curious has been demonstrated to us 

 by the study of living species from every region of the globef. 

 Many genera are peculiar to the hottest zones of continents, 

 while others, on the contrary, are found only in temperate 

 or cold regions. Hence the geographical distribution of 

 living genera and species offers to us a means of comparison 

 of the highest importance with a view to the determination of 

 the temperature of the waters in which fossil species lived, 



* Mr. Lyell has communicated to us the species which he discovered 

 in the Crag. 



-f- We are acquainted at present with ne^r\y fifteen hundred living and 

 fossil species of Foraminifers; and how many important facts may be de- 

 rived from the study of these small bodies may be seen in three works 

 which we are now publishing: 1. the Fauna of the Antilles, printed in 

 V Histoire j)oUtique, physique, et naturelle de Vile de Cuba, by M. de la Sagra ; 

 2. that of the Canaries, published in r Histoire Naturelle of those islands, 

 by Ml\I. Webb and Eerthelot; 3. the Fauna of the southern extremity of 

 America, forming a part of our Voyage dans P Amerique Meridionale. 



