in New Countries. 
5 
classified and arranged in this manner, geologists will be 
able to compare them one with the other, to establish 
well-defined bases, and make out the corresponding terms 
in each series, and tabulate the whole according to their 
united result. 
It may, perhaps, be allowed me, for the sake of the 
student of geology whose eye these remarks may happen 
to meet, briefly to mention the general principles of clas¬ 
sification now adopted by the best English geologists. 
Rocks arc divided into two great classes,—aqueous or 
sedimentary rocks, and igneous rocks, and one interme¬ 
diate or sub-class, termed metamorpliic. 
Igneous rocks are named and arranged solely from 
their mineral character: thus a crystalline compound of 
quartz, feldspar, and mica is called granite ; a rather fine 
grained mixture of feldspar and hornblende forms green¬ 
stone; a rock having a compact or finely granular base 
with diffused crystals of any mineral, is called porphyry ; 
and this without reference to their situation, or to the 
period at which they were produced. They may all, 
indeed, be of any age: granite itself, once esteemed pecu¬ 
liarly primitive, is found in the Andes more recent than 
some tertiary rocks. The nomenclature of igneous rocks, 
then, is theoretically perfectly simple, and their well- 
marked varieties are, in practice, easily ascertained. As, 
however, they have many varieties which often pass in¬ 
sensibly into each other, it is sometimes difficult or im¬ 
possible to give other than very vague or general names 
to many portions of igneous rocks. The same remarks 
will partly apply to the metamorpliic rocks: whenever 
sedimentary rocks have been so altered by heat as to 
have assumed a well-defined mineral or crystalline struc¬ 
ture, such as gneiss or mica schist, they arc apt to derive 
their names from that structure, rather than from their 
place in the chronological series. In the immediate 
