3i8 The American Geologist. May, is99 
refraction are low, the specific gravity is 2.544. The angle in- 
cluded by the prisms is 61° 30'. Extinction angle on cleavage 
(001) is not always parallel, but sometimes departs 9° from 
parallel. The undulatory extinction resembles that of sections 
of the adularia. from the dome de Gouter, of the Alps, 
which are in the laboratory .of ^Mineralogy of the Museum 
d'Histoire Naturelle, Paris. 
Locality — Monong Mine, Isle Royale. 
WoUastoiiitc. Prof. J. D. Whitney also gives two analyses 
of wollastonite, from Scoville point, Isle Royale, viz.: 
Silica 49 • 09 49 • 09 
Lime 46 . 38 44-82 
Protoxide manganese. . .48 93 
Alumina 23 i . 29 
Magnesia 14 
Water 2 . 96 2 . 96 
Carb. Acid and loss 72 90 
100.000 100.00 
He remarks that this mineral is "remarkable for its tough- 
ness, which quality it seems to possess in a higher degree than 
any known mineral." He describes this mineral as "compact, 
with uneven fracture, color light flesh red, hardness 6, lustre 
resinous to pearly, readily decomposed by acids, the silica 
separating in the form of a flocky precipitate". The water, 
dried at 100° C. was found by two determinations 2.96 and 
2.96. "Still the quantit}' seems too small to allow it to be 
considered as forming an essential part of the mineral, as it 
retains all its properties unchanged after ignition. It re- 
ceives a beautiful polish." This mineral has not since been 
reported from Isle Royale. 
Prehnitc. This is not very common, but occurs at French 
river, a few miles east of Duluth. It fills and lines numerous 
cavities, and embraces metallic copper. At Knife river it oc- 
curs in a scoria. It is more common on Isle Royale where it is 
associated with thomsonite and other zeolites and also em- 
braces metallic copper in isolated nuggets. 
Dclessitc forms small spherulites in numerous places in the 
diabasic rocks. It is sometimes wholly within some of the 
zeolites, as thomsonite, and chlorastrolite. 
