Pirsson and Washington — Geology of Red Hill, N. H. 267 



sional grains in the hornblende, but in specimens from other 

 places it sometimes is seen in the feldspars and in groups. It 

 is nowhere abundant. The average size of grain is about 

 0'25 mm , and it does not vary greatly. The apatite in its occur- 

 rence is much like the iron ore which it is apt to accompany. 

 It is in short stout prismoids, colorless and presents no unusual 

 features ; the larger crystals are about the size of the ore grains, 

 many are smaller. 



The zircon and titanite are not very common but in rough 

 crystals or grains which have a general but sparse distribution. 

 The crystals vary from 02 to 0*4 mm in diameter. The titanite 

 is very pale to colorless and but for its optical properties might 

 easily be mistaken for zircon. 



The biotite is also variable in its distribution ; in the type 

 material from the Home quarry it was observed only in small 

 shreds and flakes enclosed in the hornblende, but in other 

 places it was seen in more considerable amounts, sometimes m 

 distinct tablets in the feldspars and sometimes in minute 

 fringes about ore grains. It is deep colored and very light 

 absorbent or pleochroic, from yellow or orange to deep brown, 

 almost black or opaque. 



The pyroxenes are of several kinds; they are never an 

 importaut constituent like the hornblende. One variety is 

 a pale green, almost colorless diopside with wide extinction 

 angle occurring in small prismoids. In one case it had a gray 

 color and appeared similar to the augite found in the syenite 

 of South Norway. In some other cases it was distinctly green 

 and slightly pleochroic through assumption of the segirite 

 molecule. The last case is where it is replaced by segirite with 

 the usual characters of that mineral. Where one variety of 

 these pyroxenes occurs the others are not found; in the type 

 material only the segirite is present. The segirite is com- 

 monly attached to the hornblende and generally in distinct 

 grains embedded in its periphery and with parallel orientation 

 so that the vertical axis c and the face (100) are in common. 



The hornblende is the most important ferromagnesian min- 

 eral. Megascopically it is very black, of a good cleavage with 

 shining luster. In some places in the rock, where the grain is 

 so coarse as to almost produce a local pegmatitic facies, the 

 crystals, of a rather stout columnar habit, may be 10-20 ram in 

 length by 3-5" im in breadth, but usually they are not more than 

 a quarter of this size. 



Fragments before the blowpipe fuse at a white heat with 

 intumescence to black, shining, magnetic beads coloring the 

 flame intensely yellow, showing it to be an alkalic hornblende 

 with much iron and soda and with hydroxyl present. 



In thin sections this hornblende shows olive-brown, olive- 



