1 J.D. — on Minerals of the Lake cong sgn 
Orthoclase—In almost ave collection of Lake Superior speci- 
mens ma i seen bunches and geodes of minute reddish crys- 
tals, accompanied by native popper calcite and the zeolites, the 
usual vein-minerals of that r region; these crystals are usually 
labelled “stilbite,” but they are, in ‘reality, orthoclase, as is evi- 
dent from their physical characters and chemical Soon cl on. 
The mineral here referred to, which has, on casual inspection, 
but little resemblance to feillecia is the same one noticed on 
page 102 of our Report, where an imperfect analysis of it is 
given. The peculiar interest attaching to this anomalous occur- 
rence of the substance in question seemed a sufficient reason for. 
completing its = and adding some further remarks on its 
associations. 
This mineral occurs in minute crystals which are rarely as 
much as one-tenth of an inch in length; they are rhombic 
but not very distinct, or brilliant enough to be measured 
4 the reflecting goniometer. The angle of the prism is about 
118°, or near that of Jon J, in soairind feldspar. The termina- 
tions of these prisms are usually rough and indistinct, but formed 
by a single plane, probably 17; more frequently the ‘erystals are 
ageregated together into a confused crystalline mass, the indi- 
viduals being too minute and ill-defined to be made out without 
a magnifying glass. The mineral agrees in its physical charac- 
ters with orthoclase, fusing before the blowpipe with some diffi- 
culty to a blebby glass. 
The analysis gave: 
Silica, - - - - - - 65°45 
Alumina, - - - - - - 18°26 
Oxyd of iron, - - - - “67 
Oxyd of manganese, - - - - - trace 
Potash, : 4 : : 15°21 
