Ch. XXVI.] METAM ORPHIC ROCKS. 375 



We divide the hypogene rocks, then, into the unstratified, or 

 plutonic, and the altered stratified. For these last the term 

 ' metamorphic ' (from /xsra, trans, and //,o(p7j, 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. 



