CHAPTER XXVI. 
On the stratified rocks usually called 'primary' — Proofs from the disposition of 
their strata that they were originally deposited from water — Alternation of beds 
varying in composition and colour — Passage of gneiss into granite — Alteration 
of sedimentary strata by trappean and granitic dikes — Inference as to the 
origin of the strata called ' primary' — Conversion of argillaceous into horn- 
blende schist — The term ' Hypogene ' proposed as a substitute for primary — 
' Met amorphic' for ' stratified primary ' rocks — No regular order of succession 
of hypogene formations — Passage from the metamorphic to the sedimentary 
strata — Cause of the high relative antiquity of the visible hypogene formations 
— That antiquity consistent with the hypothesis that they have been pro- 
duced at each successive period in equal quantities — Great volume of hypogene 
rocks supposed to have been formed since the Eocene period — Concluding 
remarks. 
ON THE STRATIFIED ROCKS CALLED < PRIMARY.' 
We stated in the last chapter, that the rocks usually termed 
' primary' are divisible into two natural classes, the stratified 
and the unstratified. The propriety of the term stratified, as 
applied to the first-mentioned class, will not be questioned 
when the rocks so designated are carefully compared with strata 
known to result from aqueous deposition. 
Mode of stratification. — If we examine gneiss, which consists 
of the same materials as granite, or mica-schist which is a 
binary compound of quartz and mica, or clay-slate, or any 
other member of the so-called primary division, we find that 
it is made up of a succession of beds, the planes of which 
are, to a certain extent, parallel to each other, but which fre- 
quently deviate from parallelism in a manner precisely ana- 
logous to that exhibited by sedimentary formations of all ages. 
The resemblance is often carried farther, for in the crystalline 
series we find beds composed of a great number of layers 
placed diagonally, as we have shown to be the case in the 
