Varieties of Hornblende Slate. 



375 



sometimes fibrous. When fibrous, it is slaty ; when laminar, no slaty 

 structure can be perceived, nor any stratification, even in beds of con- 

 siderable extent. This is the rock that has been sometimes called 

 hornblende rock. (Nos. 914 to 928.) 



2. Hornblende and Feldspar. Generally the hornblende is crystal- 

 line, and the feldspar foliated, or granular ; but sometimes both ingre- 

 dients are compact, and this mixture forms a good example of primi- 

 tive greenstone. In this variety there is usually little appearance of 

 stratification, or of a schistose structure ; though this is not generally 

 true of the whole bed. And sometimes, as in Whately, where this 

 rock often assumes a columnar appearance, a schistose structure may 

 still be seen. Sometimes the feldspar in this rock, as in the west part 

 of Northfield, is finely granular, or even assumes a pulverulent ap- 

 pearance ; while the hornblende is distinctly crystalline. When the 

 ingredients are both crystalline, the rock furnishes a good example of 

 hornblende slate. This variety is usually interstratified with gneiss 

 and passes insensibly into that rock. (Nos. 929 to 951.) 



In Whately is a curious variety of hornblende slate, in which the 

 hornblende is light green and the feldspar white and compact. A 

 casual inspection would leave the impression that the rock was sien- 

 ite. But a little attention shows a very decided slaty structure. The 

 hornblende also predominates. This is the only example I have met 

 with, in which the slaty variety contains compact feldspar without 

 being porphyritic. (No. 947.) 



Associated with a large proportion of the hornblende slate in the 

 vicinity of Connecticut river, is a variety that falls under the present 

 division, that is most decidedly, and sometimes very beautifully por- 

 phyritic. The feldspar is yellowish white, between foliated and 

 granular, although sometimes retaining the form of the crystal in 

 considerable perfection. The hornblende is sub-crystalline, and in 

 the greatest quantity. Sometimes scales of mica are present. The 

 slaty structure may usually be seen in this variety, though less dis- 

 tinct than in most other varieties of this rock. There is scarcely a 

 more distinct variety of porphyry in the State than this ; and as it 

 admits of being smoothed, and probably polished, it would form un- 

 doubtedly an interesting ornamental stone. It is more common to 

 meet with this rock in rolled masses than in beds ; and hence I infer 

 that its beds are rather limited. (Nos. 944 to 946.) 



I have found a remarkable variety of this porphyritic hornblende slate 

 in Canton and Easton, near the Blue Hills, and also in Waltham, in 



