183 



gneiss, when a more accurate examination Would 

 have discovered its true nature. 



In the contact of granite with quartz rock, the 

 latter sometimes assumes a highly crystalline 

 aspect; and where the quartz rock contains fel- 

 spar, it thus becomes impossible to distinguish 

 the two, or a perfect gradation of character is 

 found. 



When granite is immediately followed by 

 hornblende schist, it happens, in the same man- 

 ner, that the character of the latter becomes more 

 decidedly granitic : it may more properly, indeed, 

 be said to become gneiss; and, as the granite, in 

 these cases, always contains hornblende, the same 

 transition takes place here as in the contact of 

 granite with other varieties of gneiss. 



The differences in the characters of granite 

 and argillaceous schist are so great, that no real 

 transition can exist between them. Yet, where 

 they have been found in contact, it has been ob- 

 served that the schist was intermingled both with 

 quartz and with felspar, so as to lose its peculiar 

 character and pass into a variety of gneiss enume- 

 rated in the synopsis of that rock. 



