Il8 The American Geologist. February, i899 
substance which resembles mesolite. The idea is suggested 
by an examination of a large number of such transitions that 
the green structureless substance is a transition stage be- 
tween chlorastrolite and mesolite, the iron element prevailing 
on one side and not on the other. It seems likely that this 
green structureless mineral may be that which has been ana- 
lyzed and named zonochlorite by A. E. Foote (Am. Assc. 
Adv. Sci., 65, 1873; Am. Jour. Sci. 1873). Probably no defi- 
nite mineral composition or structure can be detected in this 
green substance, the extremes only being identifiable, viz.. 
mesolite on one side and chlorastrolite on the other. That 
these two minerals are closely allied in origin, structure and 
composition, differing principally in the content of iron, is 
evident not only from the chemical composition and optic 
character but also from their association often in the same 
amygdule. Such association sometimes illustrates a sudden 
transition from one to the other and sometimes a gradual one. 
with a considerable amount of the amorphous green mineral. 
The re-examination of zonochlorite by Hawes (Am. Jour. Sci. 
X. 24, 1875) shows that it is not a homogeneous mineral. He 
describes it as having earthy green particles as impurities dis- 
seminated in a white mineral. Not having any opportunity 
of examining the original zonochlorite, it is only intended as 
a reasonable suggestion that it may be the same as the amor- 
phous green substance associated with the chlorastrolites of 
Isle Roy ale. 
Locality. The original zonochlorite was found by Foote 
in the amygdaloid of Nipigon bay, north shore of lake Su- 
perior. 
