J. P. Cooke, Jr., on some American Chlorites. 205 
I obtained were 27°, 26°, 19° 80’, 18°, 17°, 16°. On another 
plate beginning with an angle of 30° I next measured an angle 
of 18°. Moving the plate still farther, always lel to itself, 
the axes closed together and then again opened as I on 
to another portion of the macle. It will be noticed that the 
largest of these angles is much smaller than those observed on 
crystals of pure clinochlore, and on placing a plate of pure Kim- 
mererite behind a plate of pure clinochlore I observed not only 
that the angle between the optical axes was diminished but also 
that the color of the light transmitted through the two plates 
was precisely the same as that seen through plates of the com- 
pound crystals we have been discussing. : 
Clinochlore from Chester county, Pennsylvania.—In connection 
with the clinochlore from the Chrome Iron Mines of Texas, 
a, I have reéxamined that from the serpentine of West 
Chester in the same state. As is well known these large crys- 
“orresponding mineral from Texas. There is the same strong 
double refraction and biaxial character, the same inclination of 
4ge is not parallel but perpendicular to the edge of the hexa- 
Sonal section as is chomnda al 5. This fact first observed by 
Mr. W P. Bl : 
different plates, and I have 
= n able to find a 
Single exception to the 
Tale. oreover, this po- 
Sition of the plane of the 
the position of the plane of t 
of the se is indicated by the lines ~ 
is ideal arrangement is very nearly preserves 
Senerally we find the sia irregularities already noticed on the 
from Texas. Lastly, the dispersion is not. bane 
but lateral. This dispersion of the biaxial image is 0 | ight, 
however, that it might be readily overlooked. Itis cm 
only by a slight difference in the curvature of the rings and in 
