EXTENT OF METAMORPHISM. 



51 



Men are accustomed to look upon the solid rocks as emblems of permanency. But in 

 fact science teaches us that they are in a constant state of flux. They may be permanent 

 when measured by the life of an individual ; but when we compare their condition in the 

 different and vast geologieal periods, change is the most impressive lesson they teach ; 

 and all those changes most wisely and beneficently ordered. 



To give an idea of the extent to which rocks have been metamorphosed, we subjoin the 

 following section of the stratified rocks, with the names on the right of the azoic rocks 

 into which we know from reliable obser- 

 vation the fossiliferous to have been 

 transformed. It must not be under- 

 stood that the two kinds are generally 

 interstratified, though they are some- 

 times so ; but usually the azoic are 

 proved to be identical with the fossil- 

 iferous by following the line of their 



Alluvium. 



Tertiary. 



Chalk. 



Oolite. 



Trias. 



Permian. 



Carboniferous. 



Devonian. 



Upper Silurian. 



strike and finding a gradual change 

 from one into the other. Or when a 

 part of a formation is found to be azoic, 

 it is the lower part ; and even though 

 it be as high in the series as the tertiary, 

 none but azoic rocks will be found 

 beneath it. This shows that the met- 

 amorphic action is deep seated, and it 

 may be that the granitic and trappean 

 veins and dikes are connected with the 

 molten interior of the earth. It is 

 possible, indeed, to conceive that a bed 

 of stratified rock may be converted into 

 one unstratified, by heat and water 

 permeating upward through a sub- 

 jacent bed which is not so changed ; 

 in which case we should have granite 

 and trap independent of the molten 

 interior. But the record of geology 

 gives us few examples of this kind, 

 and the presumption, therefore, is, that 

 the unstratified rocks require for their 

 production a more powerful metamorphic action than could be communicated through 

 any other rock, without producing a correspondent change in that also. 



Lower Silurian. 



Cambrian. 



Hypozoic. 



Granitic. 



Eocene Flysch changed into Mica Schist, 

 Gneiss and 1'rotogine. 



Into Crystalline Limestone. 



Lias into Mica and Talcosc Scliist and 

 Gneiss. 



Into Talcose Schist and Gneiss. 



Into Clay Slate, Talcose Schist, Calciferous 

 Mica Schist, Gneiss and Granite. 



Into Mica Schist, Talcose Schist, Gneiss 

 and Azoic Limestone. 



Into Mica and Chlorite Schists and Gneiss. 



