CLASSIFICATION. 
43 
Silurian. So long as this name for a system of rocks is 
retained, so long will its example find imitators. 
CLASSIFICATION. 
Stratified. 
Alluvial and drift, 
Pleistocene, 
c. Kainozoic ,.. Pliocene, 
Meiocene, 
Eocene. 
Cretaceous, 
III. Hydroplastic, ... ^ b. Mesozoic , .. ■{ Lias and Oolite, 
t Trias, 
f Permian, 
| Carboniferous, 
a. Palaeozoic ,.. -{ Devonian, 
Silurian, 
Taconic. 
Lavas, Tufa, or Volcanic Pro¬ 
ducts. 
Greenstone, Porphyry, 
Basalt, Trap. 
Gneiss, Mica, Slate, Hornblende, 
Talcose Slate, £c. 
Laminated Limestone, 
Laminated Serpentine. 
Granite Sienite, 
Hypenthene Rock, Pyrocrystal- 
line, Limestone, 
Serpentine, Rensselaerite, 
Octahedral Iron Ore. 
In the foregoing arrangement, the rocks which have been 
called metamorphic and azoic by several eminent writers, have 
not been recognized as classes, or even as subdivisions of sec¬ 
tions, inasmuch as they can have no special peculiarities 
which make them applicable for such purposes. Metamor¬ 
phism occurs, or may occur, in all the series of rocks from the 
earliest to the latest sediments. It is true, the term meta¬ 
morphic has been confined to gneiss, mica slate, hornblende, 
talcose slate, &c.; but its use is theoretical, and was thus 
applied on the hypothesis that those rocks are altered sedi¬ 
ments, of which there is no evidence. The term azoic is still 
more objectionable: it presupposes that our observations have 
made certain that which from the nature of our evidence must 
ever remain doubtful. There is no doubt but that granite, 
gneiss, mica slate, &c., are azoic, but no one would think it 
proper to apply it to those rocks. 
II. Pyroplastic,. 
b. Sub aerial , 
a. Sub marine 
•{ 
f 
b. Laminated ,. -I 
I. Pyrocrystalline, •{ 
a. Massive , ... ■{ 
