18 THE MEDALS OF CREATION. Cuap. I. 
The discovery that particular fossils are confined to cer- 
tain deposits, was soon productive of important results, 
which greatly tended to the advancement of modern Geo- 
logy ; for although Dr. Lister, more than a century before, 
had obtained a glimpse of this law, its principles were 
neither understood nor regarded in this country until the 
late Dr. William Smith, by his own unaided exertions, 
proved by numerous observations on the British strata, its 
value and applicability for the identification of a deposit, in 
districts remote from each other. 
This phenomenon did not escape the notice of the distin- 
guished French philosophers, MM. Cuvier and Brongniart, 
who in their admirable work, “ Géographie Minéralogique 
des Environs de Paris,” enunciated the same principle :— 
‘Le moyen que nous avons employé pour reconnoitre au milieu 
d’un si grand nombre de lits calcaires, un lit déji observé, dans un- 
canton trés-éloigné, est pris de la nature des fossiles renfermés dans 
chaque couche; ces fossiles sont toujours généralement les mémes 
dans les couches correspondantes, et présentent d'un systéme de 
couche & un autre systéme, des différences d’espéces assez notables. 
C’est un signe de reconnoissance qui jusqu’a présent ne nous a pas 
trompés.” * 
Now, though recent discoveries have shown that this rule 
has many exceptions, and that its too stringent adoption 
has been productive of some erroneous generalizations, yet 
if employed with due caution it is fraught with the most 
interesting results, and is the only certain basis of our know- 
ledge respecting the appearance, continuance, and extinc- 
tion, of the lost races of animals and plants, which were once 
denizens of our planet. 
In the “ Wonders of Geology” will be found a compre- 
hensive sketch of the composition and arrangement of the 
several formations or groups of strata; and a reference to 
that work will afford the student the necessary information 
* Géog. Min. Oss. Foss. tom. ii. p. 266. 
