20 NATURA T HISTORY OF 



is drawn the value of a clear view of the facts belong- 

 ing to the cavern and loam deposits of organic remains, 

 without as well as with human bones, and the so called 

 petrified skeletons of man which have been detected on 

 various occasions ; hence also the interest attached to 

 the changes which have occurred on the earth's sur- 

 face, because they may have had a paramount influence 

 on the primeval distribution of man, and constitute the 

 only additional question which philosophical research 

 can attach to the primordial history of the human 

 species. At a later period, minor catastrophes, and 

 the action of human passions, led to known migrations 

 by sea, and to the progress of colonization by land. If 

 the most remote, were causes of the approximation of 

 different species of man, or of the separation of the 

 three great varieties of the human race, taken as a 

 single species, the later were most certainly the source 

 of the minor distinctions, which do exist both between 

 nations of different types and of the same original 

 stem. 



Although the question of the unity of species, that 

 is, whether mankind is to be regarded as a genus, con- 

 stituted of three or more species, or as only one, com- 

 posed of as many, or of a greater number of varieties, 

 subdivided into races, may never be positively decided ; 

 it will not the less remain an inquiry, of intense in- 

 terest, to trace the several conditions, which, in zoology, 

 are assumed to have a preponderating influence : there- 

 fore, researches directed to the questions, whether the 

 differences of conformation are sufficient in their ana- 



