28 



ent shades of red and pink are very common, and green and 

 other tints are frequently met with. Feldspars of several dis- 

 tinct colors are sometimes commingled in the same hand speci- 

 men. A beautiful granite occurs in West Dedham and Dover, 

 for example, in which the feldspar is chiefly of a light-green 

 color, but contains interspersed through it numerous crystals of 

 a flesh-red feldspar. Such instances are common, especially 

 among the granites in Dedham and Dover, and along the 

 Swampscott shore. The occurrence of masses of red and white 

 granite on the south-western end of Marblehead Neck, in close 

 juxtaposition, but not blended, is well known, and has been 

 noted by Dr. Hunt, Prof. Hyatt, and other observers. The 

 hornblende of the granites presents a variety of aspects, fre- 

 quently having a greenish-slaty, or chloritic appearance ; and it 

 is probable that our Huronian granites are often, locally, of the 

 variety called "protogine" by the French geologists.^ It is 

 worthy of note that the Huronian granites of Eastern Massa- 

 chusetts are usually destitute of mica, the micaceous granite of 

 Eockport and Gloucester, to which attention has been specially 

 directed by Mr. M. E. Wadsworth,^ probably constituting the 

 single notable exception. 



These granites, as every observer well knows, are subject to 

 extensive variation in both texture and composition, and the va- 

 rieties are so numerous, pass into each other so frequently, and 

 are so perfectly blended, that their distinction on the map 

 would be, at least in the present state of our knowledge, a 

 hopeless task, and I have not attempted it. Since, however, 

 there is such a deficiency of definite knowledge concerning the 

 geographic relations of the diflerent varieties of granite, even a 

 general sketch of the distribution of the leading types may 

 prove useful as a basis for future observations. For this 

 purpose I will consider the granites as embracing three principal 

 varieties. These are, (1) the coarsely crystalline, little horn- 



1 According to Prof. Haughton, the green mineral of protogine is never talc, but 

 usually chlorite, or some kindred mineral. 



2 Proo. Bost. Soo. Nat. Hist., xix., 309. 



