G. W. Hawes—Zonochlorite and Chlorastrolite. 25 
those which were very plainly banded with white he considered 
impure. But thin sections of some of the dark green stones, 
received from Prof. Foote, and considered by him as the purest 
zonochlorite, when examined under the microscope, show that 
these, like the other specimens, are more or less banded and 
consist of green earthy particles disseminated through a white 
mineral, ark green specimen gave me, on analysis, the 
following composition : 
POD oo nk ob oh 5S  FAREREAEEES ES Ce 
OMNI we Poo ie cae dees candace ces 19°41 
POI Use SS Ss eee ep eee 6°80 
wreeroth daides: 056 us ec Poe ccecd iawe 4°54 
bie Pep a PE ee 22°77 
MaONElA ote Se 2°48 
PEM hc See Fe ee Ve eee trace 
Wit. cioh5, Nal a BS ee 
100°34 
The analysis indicates that the mineral is a very impure 
variety of prehnite, a mineral which is common in the trap 
of that region ; and its hardness and behavior before the blow- 
pipe point to the same conclusion. The analytical results ob- 
tained by Prof. Foote show that the material he examined was 
not homogeneous, as he states that the percentage of water, the 
average of which was 8-7, varied from 1-03 to 12°9. The pres- 
— of magnesia shows that a portion of the impurity is chlo- 
rite. 
* Boston Journal of Natu 3 
; ral History, vol. v, p. 488. Report on the Geology 
acre Superior Land District, Part II, p. 97. Dana’s Mineralogy, 5th edi- 
