The Scope of Paleontology. — Williams. 149 
'Principles of Geology'], 1 conceived the idea of classing the 
whole of this series of strata according to the different degrees 
of affinity which their fossil Testacea bore to the living forms. 
Having obtained information on this subject during my travels 
on the continent, 1 learned that M. Deshayes of Paris, already 
celebrated as a Conchologist, had been led independently, by 
the study of a large collection of recent and fossil shells, to 
verj' similar views respecting the possibility of arranging the ter- 
tiary formations in chronological order, according to the propor- 
tional number of species of shells identical with living ones, which 
characterized each of the successive groups above mentioned. " 
The view of M. Deshayes may be given in the words of Robert 
Bakewell, as found in the 5th edition of his geology (p. 399, 
1838). He writes: 
"M. Deshayes considers that the relative ages of different 
groups of strata or formations may be determined by their zoolog- 
ical characters alone; that is, by the species of shells they con- 
tain. He forms two grand divisions of stratified formations: 
1 . Those which contain no species of shells analogous to exist- 
ing species [meaning identkal species]. This division is stated 
to comprise all the secondary strata. 2. Strata which contain a 
greater or lesser number of species analogous to existing species. 
The last division comprises all the tertiary formations. Again 
he subdivided this division into three groups, according to the 
greater or lesser proportion of species of shells that they each 
contain analogous to living species." (Bakewell's Introduction 
to Geology, p. 399). 
The law here propounded is quite different from that announced 
by William Smith. "That each stratum contained organized 
fossils peculiar to itself, and might, in cases otherwise doubtful, 
be recognized and discriminated from others like it, but in a differ- 
ent part of the series, by examination of them." (Phillips' 
Memoirs of William Smith, p. 15.) 
Smith's law considers only the significance of fossils as marks 
indicating the stratum to which they belong. Fossils studied 
and described on this basis, are at best but "Medals of Creation," 
i. e., the classified signs by which geological formations may be 
recognized. This is the scope of the older paleontology. The 
higher or comparative paleontology as set forth by Deshayes, 
Lyell and Lonsdale considers the relationship which fossils bear 
to each other, to those which preceded them and to their succes- 
