INFERENCES. 



47 



succeed one another in the following order : mica schist, granite, fossiliferous limestone 

 (Devonian), granite, mica schist, granite, schist, limestone, schist, &c. Some of these 

 masses, especially the granite, may be somewhat wedge-shaped, especially as we follow on 

 in the direction of the section. The mica schist is highly crystalline, containing that 

 peculiar species of mica denominated Adamsite, by Prof. Shepard. 



Fia. 19. 



Clay Slate. 

 Clyde River. 



Granite, Mica Schist, and Limestone. Derby. 



Here we have highly crystallized granite and mica schist lying above limestone of De- 

 vonian age, in which we find encrinal stems, and it is scarcely at all crystalline. But this 

 might take place, either by the greater fusibility of the super-imposed and. intercalated 

 beds, or possibly by a lateral permeation of heat and water. 



2. The process of metamorphism is still going on. We see it more strikingly at the sur- 

 face, especially in regions that have not experienced the erosions of the drift agency. 

 There the rocks are manifestly changed, often to the depth of several feet. But when we 

 open the most solid rocks, or descend into the deepest mines, we shall find minerals un- 

 dergoing alteration new ones taking the place of old ones. Wherever water penetrates, 

 even though the temperature be not raised, we may expect metamorphism. Indeed 

 Bischof regards these changes as universal. "All rocks," says he, "are continually sub- 

 ject to alteration, and their sound appearance is not any indication that alteration has not 

 taken place." (Vol. III., p. 426.) If it be so, it shows us how wide and difficult is the 

 field which lies open for geological research. 



3. Metamorphism shows us that tlie earliest formed rocks on the globe may have all disap- 

 peared. If we suppose, what geologists now generally admit, that the globe has cooled 

 from a molten state, the earliest formed crust may have been a granite rock. True, this 

 crust as a general fact has been thickening. But the process in many places, and perhaps 

 alternately all over the globe, has been reversed. Suppose by the slow power of erosion, 

 materials have accumulated in the bottoms of the oceans to a great thickness ; the effect 

 would be to cause the line of fusion to ascend, it may be so far as to melt off all the rocks 

 originally deposited. In other places erosion might have worn off the upper part of this 

 crust, and though this would cause the line of fusion to descend, and thus add new rock, 

 yet between these agencies above and beneath, continued through countless ages, none of 

 the first formed crust may remain. Or if any of it is left, it would be impossible to 

 distinguish it from .subsequent formations. So that the idea of a primary granite, or any 

 other rock, in the strict sense of the term, has no foundation in nature. 



4. Metamorphism furnishes the most plausible theory of the origin of the azoic stratified rocks, 

 which are mica, talc, and Jiornblende schists, gneiss, serpentine, white limestone, &c., such as cover 

 a large part of Vermont. The hypothesis that these rocks were deposited in a crystalline 

 state, in an ocean so hot that the materials would crystallize, is not consistent with what we 



