376 METAMORPHIC ROCKS. [Ch. XXVI. 



That expectation has not been realized ; yet was it more rea- 

 sonable than the doctrine of the universality of certain rocks 

 which were admitted to be of sedimentary origin ; for there is 

 certainly a remarkable identity in the mineral character of the 

 hypogene formations, both stratified and unstratified, in all 

 countries ; although the notion of a uniform order of succession 

 in the different groups must be abandoned. 



The student may, perhaps, object to the views above given 

 of the relation of the sedimentary and metamorphic rocks, on 

 the ground that there is frequently, indeed usually, an abrupt 

 passage from one to the other. This phenomenon, however, 

 admits of the same explanation as the fact, that the beds of 

 lakes and seas are now frequently composed of hypogene rocks. 

 In these localities the hypogene formations have been brought 

 up to the surface and laid bare by denudation. New sedimen- 

 tary strata are thrown down upon them, and in this manner 

 the two classes of rocks, the aqueous and the hypogene, come 

 into immediate contact, without any gradation from one to the 

 other. As we suppose the plutonic and metamorphic rocks to 

 have been uplifted at all periods in the earth's history, so as to 

 have formed the bottom of the ocean and of lakes, by the same 

 operations which have carried up marine strata to the summits 

 of lofty mountains, we must suppose the juxtaposition of the 

 two great orders of rocks now alluded to, to have been a neces- 

 sary result of all former revolutions of the globe. 



But occasionally a transition is observable from strata con- 

 taining shells, and displaying an evident mechanical structure, 

 to others which are partially altered, and from these again we 

 sometimes pass insensibly into the hypogene series. Some of 

 the argillaceous-schists in Cornwall are of this description, being 

 undistinguishable from the hypogene schists of many countries, 

 and yet exhibiting, in a few spots, faint traces of organic re- 

 mains. In parts of Germany, also, there are schists which, 

 from their chemical condition, are identical with hypogene- 

 schists, yet are interstratified with greywacke, a rock probably 



