362 W. Cross — Some secondary minerals 



sides in many cases. The illustrations give the form of the 

 massive material with strictly uniform orientation. Sharp 

 pointed spires without attached needles are seen. In fig. 2 the 

 brown hornblende extinguishes at 9° 35' to the left of the daxis, 

 which is indicated by cleavage, while the blue extinguishes at 

 12° 45' to the right. These are not maximum values, hence the 

 section is clearly somewhat inclined to the plane of symmetry. 

 In fig. 3 is represented a section more nearly parallel to the 

 clinopinacoid of a brown hornblende prism which has been 

 partially replaced by blue amphibole at the lower end and by 

 actinolite at the upper. In this section the brown hornblende 

 extinguishes at 10°40 / to the left of the cleavage line and the 

 blue at 13° to the right. Certain cleavage lines run uninter- 

 ruptedly through both minerals, and, as proven by all orientated 

 sections, the axes 6 and b are plainly common to the two va- 

 rieties. Fig. 4 gives a representation of a brown hornblende 

 crystal to one end of which the blue amphibole has been added, 

 while on the other end actinolite of pale grass-green color 

 forms a similar extension and is itself tipped by the blue 

 variety. The spire of blue amphibole is fringed by imperfectly 

 oriented needles of the same substance in a manner very 

 roughly represented by the figure and the bounding surfaces 

 do not appear to be regular crystal planes. In optical orienta- 

 tion tke blue portions of the two extremities are plainly identi- 

 cal, extinguishing at 13° to the right of the cleavage lines of 

 the main hornblende crystal, while the latter and the added ac- 

 tinolite extinguish in common at 10° to the left. Fig. 5 repre- 

 sents a crystal of amphibole, cut nearly parallel to the clinopina- 

 coid, in which three substances are sharply distinguished. At 

 the lower end is the normal brown hornblende, extinguishing 

 at 14° 30' to the left of the axis 6. Adjoining this is actinolite, 

 the line between the two being straight in part and apparently 

 representing a crystal plane. This actinolite extinguishes at 

 15° 3<J / to the left of 6, and while the part near the brown is 

 grass-green the upper portion is colorless, the line between be- 

 ing sharp and parallel to the same apparent crystal planes as 

 the other change. On the upper end of the crystal is an area 

 of dark chestnut-brown color extinguishing at about 8° to the 

 left from the cleavage lines, some of which run uninterruptedly 

 through both the actinolite and the brown mineral. Absorp- 

 tion is very strong near the axis c, so that the angle of extinc- 

 tion cannot be closely measured Beyond this peculiar brown 

 mineral there are tufts of fine blue needles some of which are 

 orientated parallel to the vertical axis of the large crystal. They 

 spring from the actinolite as well as from the brown amphibole, 

 and also lie free in the calcite surrounding the crystal. While 

 these needles do not show uniform orientation the parts of the 



