Thalitc and Bozvlingite from Lake Superior. — Wi?ichell. 43 
in sections showing the fibres cut transversely, and, owing to 
the extreme fineness, requires the use of the immersion object- 
ive. 
These characters isolate thalite from the vermicular 
chlorites and from kaolinite, from the former in having its bi- 
sectrix parallel with the fibration instead of perpendicular, 
from the latter in having a positive instead of a negative bisec- 
trix. The chemical composition, determined by Owen, shows 
a marked divergence from that of saponite. especially if the 
supposed new substance be considered; and as determined by 
Mr. L. B. Pease, of the University of Minnesota, is as follows: 
Co/nposition of thalite. 
S iO. 42.38 
ALO3 7-37 
Fe»03 2.65 
MgO 23.29 
CaO 552 
K.O 19 
Na.O . 36 
H.O (at 100° 10.38) 18.18 
Total 99-94 
Localities of thalitc. Knife river: at half way between 
Knife river and Agate bay ; Gooseberry river. 
Bozvli?igite. In numerous instances an alteration of ol- 
ivine has produced a mineral which grows in place of the oliv- 
ine itself and approximately takes its form, whereas the fore- 
going are found in larger masses where it is probable olivine 
never existed. This mineral is darker colored, being green- 
ish brown or yellowish. Taking the place of olivine it appears 
like an original mineral earlier than the feldspars and the 
augites ; when cut favorably it shows two cleavages, but usual- 
ly only one, and it then is distinctly and rather strongly ab- 
sorptive, the darker shade recurring when the cleavage is par- 
allel with the principal section of the polarizer. It can easilv 
be mistaken for chlorite, when it is not well formed. It is not 
fibrous, but is cleaved parallel to definite crystallographic char- 
acters. The optic plane is perpendicular to the easy cleavage, 
and the acute bisectrix (//p) is shown in sections parallel to this 
cleavage. The axial angle is small, and the interference figure 
is almost a permanent black cross. In sections transverse to 
