Ch. XXVI.] 
MET AMORPHIC ROCKS. 
375 
We divide the hypogene rocks, then, into the unstratified, or 
plutonic, and the altered stratified. For these last the term 
' metamorphic ' (from i^zta, trans, and [xo^n, form) may be 
used. The last-mentioned name need not, however, be often 
resorted to, because we may speak of hypogene strata, hypo- 
gene limestone, hypogene schist, and this appellation will suffice 
to distinguish the formations so designated from the plutonic 
rocks. By referring to the table (No. I.) at the close of this 
chapter, the reader will see the chronological relation which we 
conceive the two classes of hypogene rocks to bear to the strata 
of different ages. 
No order of succession in hypogene formations. — When we 
regard the tertiary and secondary formations simply as mineral 
masses uncharacterized by organic remains, we perceive an 
indefinite series of beds of limestone, clay, marl, siliceous sand, 
sandstone, coal, and other materials, alternating again and 
again without any fixed or determinate order of position. The 
same may be said of the hypogene formations, for in these a 
similar want of arrangement is manifest, if we compare those 
occurring in different countries. Gneiss, mica-schist, horn- 
blende-schist, quartz rock, hypogene limestone, and the rest, 
have no invariable order of superposition, although, for reasons 
above explained, clay-slate must usually hold a superior posi- 
tion relatively to hornblende schist. 
We do not deny, that in a particular mountain-chain, a 
chronological succession of hypogene formations may be recog- 
nized, for the same reason that in a country of limited extent 
there is an order of position in the secondary and tertiary 
rocks, limestone predominating in one part of the series, clay 
in another, siliceous sand in a third, and so of other compounds. 
It is probable that a similar prevalence of a regular order of 
arrangement in the hypogene series throughout certain dis- 
tricts, led the earlier geologists into a belief, that they should 
be able to fix a definite order of succession for the various 
members of this great class throughout the world. 
