374 



IIYPOGENE ROCKS. [Ch.XXVI. 



district, the lowest of these will be converted into hornblende- 

 schist, while the uppermost may continue in the condition of 

 clay -si ate. 



The term 'Ilypoyrne ' proposed for Primary. If our readers 

 have followed us in the train of reasoning explained in this and 

 the preceding chapter, they must already be convinced that 

 the popular nomenclature of Geology, in reference to the so 

 called ' primary ' rocks, is not only imperfect, but in a great 

 degree founded on a false theory ; inasmuch as some granites 

 and granitic schists are of origin posterior to many secondary 

 rocks. In other words, some primary formations can already 

 be shown to be newer than many secondary groups a mani- 

 fest contradiction in terms. 



Yet granite and gneiss, and the families of stratified and 

 unstratified rocks connected with each, belong to one great 

 natural division of mineral masses, having certain characters in 

 common, and it is therefore convenient that the class to which 

 they belong should receive some common name a name which 

 must not be of chronological import, and must express, on the 

 one hand, some peculiarity equally attributable to granite and 

 gneiss (to the plutonic as well as the altered rocks), and which, 

 on the other, must have reference to characters in which those 

 rocks differ both from the volcanic and from the unaltered 

 sedimentary strata. We propose the term ' hypogene ' for this 

 purpose, derived from VTTO, subter, and yjvcpoai, nuscor, a word 

 implying the theory that granite and gneiss are both netlicr- 

 formed rocks, or rocks which have not assumed their present 

 form and structure at the surface. It is true that gneiss and 

 all stratified rocks must have been deposited originally at the 

 surface, or on that part of the surface of the globe which is 

 covered by water; but according to the views explained in this 

 and the foregoing chapter, they could never have acquired 

 their crystalline texture, unless acted upon by heat under pres- 

 sure in those regions, and under those circumstances where 

 the plutonic rocks are generated. 



Tku 1 1.' nn ' Melanwrphic ' yrupuscd fur stratified primary* 



