of several American Micas. 345 



are easily measured. Those doubtful cases now under con - 

 sideration are probably referable to an oblique crystalline 

 form ; but even here the study of a large number of speci- 

 mens from the same locality is required before satisfactory 

 inferences may be drawn. To this head I refer the deep 

 reddish copper-coloured mica from Franklin Furnace, Sussex 

 Co., New Jersey, which is found in white dolomite ; also a 

 mica of similar character from St Jerome, Canada ; and that, 

 well known to collectors, from Moriah, in Essex Co., N. Y., 

 which is more remarkable than any I have seen for its deep 

 smoky-red colour, as seen by transmitted light. But the 

 most interesting specimens of this sort observed by me, are 

 certain large crystals of a deep olive-green colour, from the 

 Yale College cabinet, and which in our investigations have 

 been referred to Monmouth, N. J., although their true loca- 

 lity is still doubtful. This mica is in very large rhombic 

 crystals, oblique from an obtuse edge. P : M = 112° — 115J°, 

 M : M = 122°- 125°, the angle of the basal edges is 119° 30'. 

 Plane angle of P 119°. It has a cleavage parallel to the 

 longer axis. The obliquity of the optic axes appears to be 

 nearly as great as that seen in some phlogopites of equal 

 thickness, but the dark colour of the mineral prevents a sa- 

 tisfactory examination. Should the character of this mica 

 be confirmed by a set of good analyses, it must in all proba- 

 bility form a distinct species, as suggested by Dana.* This 

 variety is not to be confounded with the well crystallised 

 mica of Greenwood Furnace, which, as seen in ordinary spe- 

 cimens, is oblique from the acute edge (sections of distorted 

 acute rhombohedrons), and which is regarded as a uniaxial 

 mica. 



Euphyllite, margarodite, and emerylite, have hitherto been 

 found in quantities too inconsiderable, and in specimens ge- 

 nerally too poorly crystallised, to furnish many measure- 

 ments, t 



( To be concluded in our next Number.) 



* Mineralogy, p. 690. 



t For the composition of these species, see Dana's Mineralogy. 



I 



