Optical Examination of several American Micas. 381 
the accompanying-tables we have given for each specimen: Ee 
In 
measured, its locality, color, the source whence. received, the 
angle bate the optic axes, and other observations bearing on 
their history. It may afford a more correct impression of the pres- 
ent state of this investigation to remark that specimens from over 
one hundred American localities of mica have been examined be- 
sides a considerable number of uncertain locality ; and from many” 
of these localities very numerous specimens have been measured. 
Thus there have been measured of muscovite specimens from 
about 50 localities; of phlogopite over 30; of euphyllite 2; of 
fort Bs of biotite about 12, and: ‘of doubtful species : 
: —The number of localities in the toiled States fitke : 
tihng aman mica (biotite) has been constantly diminishing 
since the commencement of these- investigations, as increased 
skill in observation and improved’ means of examination have 
shown one after another of the reddish and yellow or brown. 
colored micas to have more or less decidedly the characters of 
phlogopite.' <2 
Thus the dark brown mica of Fine, the red micas of M - 
of Sterling, of Franklin, and of Gouverneur, have successis ly 
_ been thrown out of the list of biotites into the binaxial species. 
Others remain in doubt as those of Topsham, Me., and a Pa. 
reenwood Furnace, comet wig Orange County, N, Y., is the 
oe nates to this variety also. It is opake in plates over 
malin of an inch thick, but of rich olive green in thin 
plat 
ay 
hai but not so much so a as to require any ba 
a 
new analysis of this variety in progress the results of which he 
will present on a future occasion. The chemical constitution of 
_ Very few American biotites has been cua: indeed the local- 
ity just referred to is the only one cited. Von Kobell’s result 
Corresponds with the formula given on page 375. 
ss Mica of Monroe, N. ¥.—This mica from the same town as 
= last is also uniaxial and gives a figure almost entirely cir- 
* in, ¥. P. 81. + Min. (1850), 360. 
