LIFE ON THE EARTH. 197 



so as to appear to be hereditary, has seldom been 

 rejected as a specific character; even colour and 

 magnitude are not despised in this analysis. 



But in Palaeontology the list of species is even less 

 satisfactory. For here the question of descent is 

 seldom to be insisted on at all; very often we have 

 only the knowledge of one age of the fossils, some- 

 times only one specimen occasionally only the sur- 

 face of that. For the purpose of diminishing these 

 sources of error, and of determining in regard to 

 each species the two most important parts of its 

 history, viz. 



1. Its geographical province, the area which it 



occupies, in one stratum or in several strata ; 



2. Its geological range in differents parts of this 



area; 



nothing is so effectual as those monographs of par- 

 ticular well selected districts, which are founded on 

 accurate observations of the localities of fossils, and 

 of the conditions under which they are observed. 

 But these observations lose all their value if the 

 species of fossils be not precisely and certainly de- 

 termined, and this amidst the conflict of classifica- 

 tions, and unequal estimates of specific agreements 

 and differences, is a condition of success not always 

 easy to be secured. If for example we wish to trace 

 the geographical province or geological range of a 



