THE EOZOIC AGES. 21 



recent geological formations. Yet the difference is 

 one in condition rather than composition. The 

 members of this ancient aristocracy of the rocks 

 are made of the same clay with their fellows, but 

 have been subjected to a refining and crystallizing 

 process which lias greatly changed their condition. 

 They have been, as geologists say, metamorphosed; 

 and are to ordinary rocks what a china vase is to 

 the lump of clay from which it has been made. 

 Deeply buried in the earth under newer sediments, 

 they have been baked, until sandstones, gravels, and 

 clays came out bright and crystalline, as gneiss, 

 mica-schist, hornblende-schist, and quartzite — all 

 hard crystalline rocks showing at first sight no 

 resemblance to their original material, except in the 

 regularly stratified or bedded arrangement which 

 serves to distinguish them from igneous or volcanic 

 rocks. In like manner certain finer, calcareous sedi- 

 ments have been changed into Labrador feldspar, 

 sometimes gay with a beautiful play of colour, and 

 what were once common limestones appear as cry- 

 stalline marble. If the evidence of such metamor- 

 phoses is asked for, this is twofold. In the first 

 place, these rocks are similar in structure to more 

 modern beds which have been partially metamor- 

 phosed, and in which the transition from the unaltered 

 to the altered state can be observed. Secondly, 

 there are limited areas in the Laurentian itself, in 

 which the metamorphism has been so imperfect as 

 to permit traces of the original character of the rocks 



