COMrONEXT MINERALS. 85 



accompanied bv clouds of leucoxene. The appearance of tliis nmtcrial is 

 entirely accordant with the supposition that it is granular titanite. 



Titai.ite. — Besides tlie clastic grains of this mineral in the sandstones, it 

 ap[)eai's in tlie glaucophane schists in characteristic rhoudjoid forms, the 

 corners being wholly unabraded. In the same rocks it appears as more or 

 less regular grains, embedded in zoisite and in entirely undecomposed glau- 

 cophane. It is thus to be considered as an authigenetic component of these 

 rocks, apparently replacing the ilmenite of the granular group. The colors 

 in ordinary and in polarized liglit and the other optical properties, as well ns 

 the form, are entirely characteristic and require no comment. 



Apatite. — This mineral having been detected by optical and chemical 

 means as an authigenetic constituent in one slide, a special examination of 

 the collection was made for fear that it might have been mistaken for zoisite. 

 It was found in abundance in some of the pyroxene granular rocks and in 

 two glaucophane schists. Minute prisms of this mineral appear also to be 

 present in a few of the altered sandstones. Apatite is tolerably frequent as 

 an inclusion in clastic grains. 



chiorites. — Chlorites are abundant both in the sandstones and in the 

 recrystallized rocks which are undergoing weathering. As usual, it is dif- 

 ficult to determine the particular species of chlorite ; indeed, the specific 

 distinctions between these minerals are far from satisfactory. All of the 

 chlorite met with possesses the usual grass-green tint and is strongly di- 

 chroitic. It is usually fibrous, but in a few cases shows irregular scales. 

 The fibers always extinguish light when sensibly parallel to the principal 

 secti(in of the polarizing apparatus, while some of the scales appear to 

 remain absolutely dark between crossed nicols. The interference colors of 

 the fibrous aggregates vary greatly. When the mass is composed of felted 

 libers of minute size the colors of polarization are very feeble. In other 

 cases dark-blue tints appear, and in some instances, wdiich appear to be 

 distinguished by unusually large quantities of parallel individuals, yellow 

 interference colors make their appearance. By treatment through a per- 

 forated cover with moderately strong, warm chlorhydric acid, it was found 

 that the ordinary fibrous chlorite of these rocks is not attacked. Portions 

 of the same specimens, however (e. g , No. 26, Sulphur Bank), treated with 



