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 

 ' Metamorphic' 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 sf ratification. 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 



