332 
SECONDARY FORMATIONS. 9 
[Ch. XXIII. 
groups of strata above enumerated by us, names were given to 
each, derived from the mineral composition of the rocks in 
those parts of Germany, England or France, where they hap- 
pened to be first studied. When it was afterwards acknow- 
ledged that the zoological and phytological characters of the 
same formations were far more persistent than their mineral 
peculiarities, the old names were still retained, instead of being 
exchanged for others founded on more constant and essential 
characters. The student was given to understand, that the 
terms chalk, green- sand, oolite, red marl, coal, and others, 
were to be taken in a liberal and extended sense; that chalk 
was not always a cretaceous rock, but, in some places, as on the 
northern flanks of the Pyrenees, and in Catalonia, a saliferous 
red marl. Green-sand, it was said, was rarely green, and fre- 
quently not arenaceous, but represented in parts of the south 
of Europe by a hard dolomitic limestone. In like manner, it 
was declared that the oolitic texture was rather an exception 
to the general rule in rocks of the oolitic period, and that no 
particle of carbonaceous matter could often be detected in the 
true coal formation of many districts where it attains great 
thickness. It must be obvious to every one, that inconvenience 
and erroneous prepossessions could hardly fail to arise from 
such a nomenclature, and accordingly a fallacious mode of rea- 
soning has been widely propagated, chiefly by the influence of 
a language so singularly inappropriate. 
After the admission that the identity or discordance of 
mineral character was by no means a sure test of agreement or 
disagreement in the age of rocks, it was still thought, by many 
geologists, that if they found a rock at the antipodes agreeing 
precisely in mineral composition with another well known in 
Europe, they could fairly presume that both are of the same 
age, until the contrary could be shown. 
Now it is usually difficult or impossible to combat such an 
assumption, on geological grounds, so long as we are imper- 
fectly acquainted with the geology of a distant country, inas- 
much as there are often no organic remains in the foreign 
