AMERICA THE OLD WORLD. 
I 4 
neous character were by no means exclusively 
characteristic of the earliest times, they are now 
classified together upon very different grounds 
from those on which geologists first united them ; 
though, as the name Primary was long retained, 
we still find it applied to them, even in geo- 
logical works of quite recent date. This defect 
ot nomenclature is to be regretted, as likely to 
mislead the student, because it seems to refer to 
time ; whereas it no longer signifies the age of 
the rocks, but simply their character. The name 
Plutonic or Massive rocks is, however, now al- 
most universally substituted for that of Primary. 
A wide field of investigation still remains to be 
explored by the chemist and the geologist to- 
gether, in the mineralogical character of the 
Plutonic rocks, which differs greatly in the dif- 
ferent periods. The earlier eruptions seem to 
have been chiefly granitic, though this must not 
be understood in too wide a sense, since there 
are granite formations even as late as the Terti- 
ary period; those of the middle periods were 
mostly porphyries and basalts; while in the more 
recent ones, lavas predominate. We have as yet 
no clue to the laws by which this distribution of 
volcanic elements in the formation of the earth is 
regulated ; but there is found to be a difference 
in the crystals of the Plutonic rocks belonging 
to different ages, which, when fully understood, 
