18 J.D. Whitney on Minerals of the Lake Superior region. 
their size, color, and general habit. They are rarely more than 
a few hundredths of an inch in length, have the same crystalline 
form, and are, with rare exceptions, of a light reddish color. 
Feldspar, in no instance, so far as has yet been observed, forms 
the bulk of the veinstone; it is only met with in comparatively 
minute quantity, although occurring in numerous localities. 
Only a single instance has been noticed where a crystal had a 
length as great as one-tenth of an inch, and this was an imper- 
fectly formed one. 
Note.—Weissigite, described by Jenzsch, is undoubtedly or- 
thoclase, as suggested in Dana’s Mineralogy, p. 513; this was 
found in a porphyritic amygdaloid, with chalcedony and quartz, 
and is spoken of by Jenzsch as the first known instance of the 
occurrence of a feldspathic mineral in an amygdaloidal cavity 
of a rock of this class. 
Serpentine.—W ell-characterized serpentine has not yet been 
found in the Lake Superior region; but a substance closely re- 
lated to this mineral, and, in fact, differing from it chiefly by 
the substitution of protoxyd of iron, in a large but varying 
amount, for a portion of the magnesia, forms the head-land of 
Presquw’ isle, near Marquette. An imperfect analysis of this rock 
given in Foster and Whitney’s Report, Part II, page 92. 
_ Since the publication of that analysis new specimens have been 
collected, and a more thorough examination made of it, of which 
the results here follow. : 
The substance is of a deep green color, so deep as to appear 
almost black; its powder is light greenish-gray. Its hardness 
is a little above that of common serpentine. It is readily at- 
tracted by the magnet, when broken into small fragments. In 
some specimens minute octahedral crystals of magnetic iron ore 
disseminated through the mass can be seen with the aid of the 
magnifying glass. ‘The substance is readily attacked by chloro- 
hydric acid, even in thé-cold, if finely pulverized; but a small — 
~ of unattacked mineral remains behind when the insolu- 
le residuum is treated with carbonate of soda in the usual way. 
It amounts to from two to six per cent, and appears to be an in- — 
soluble silicate mechanically mixed with the serpentine; it 18 
probably hornblende, but has not been analyzed. 
The analyses of three specimens collected at some distance 
from each other, gave the following results, as the composition 
of the soluble portion of the substance: 
ia > 7 
= Bilica, 86-95” 3125 
- ‘Magnesia, 33-07 28°6 14°83 
Soda, 97 116 a 
_ Protoxyd of iron, 14-14 19: 
_ Peroxyd of iron, t gio 6°15 12°90 
Water, = Youo =. 10-89 
