NEW ANALCITE ROCK FROM LAKE SUPERIOR 433 
just referred to are embedded. It is clear and transparent, with 
some dusty spots, however, and has not the look of ordinary 
volcanic glass. With high powers a delicate, but distinct, sys- 
tem of cubic cleavage lines can be seen, proving that the mineral 
is isometric and therefore probably analcite, though no crystal 
forms were observed. 
An attempt was made to isolate the glassy mineral with a 
heavy solution, analcite being lighter than any other rock form- 
ing mineral belonging to eruptives, and it was found that 17 
per cent. of the powder floated when gypsum was used as an 
index (spec. grav. 2.32); but when examined with the micro- 
scope the powder was found to contain doubly refracting por- 
tions embedded in the isotropic ones, and some isotropic portions 
were noticed associated with the heavier minerals. Some of the 
rock was then treated with strong hydrochloric acid, when 
partial gelatinization took place, and it seemed wise to reduce 
the whole to dryness to render the silica insoluble. It was 
found that 27.76 per cent. of the whole weight went into solution, 
omitting, of course, the silica of the mineral which gelatinized 
when treated with acid. A second portion treated in the same 
way asa check gave 30.35 per cent. of soluble matter. Probably 
the first portion taken contained more of the sphaerulitic parts 
than the second. An analysis of the soluble part made by myself 
gave the following results: 
Al,O3 - - - . 10.90 
Fe,Q,; - - . Bale 
CaO - - - - 108 
MgO - - - trace 
Na,O_ - - - - 6.60 
K,0O - - - - not det. 
H,0O (at 100°) - - 69 
H,O (at red heat) -- 4.85 
CO, - - - - 93 
28.13 
We may assume that the only minerals in the rock which 
would be appreciably dissolved by HCl are analcite, limonite, 
