348 The American Geologist. December, i89J< 
Localities of Tliomsonitc. Probably Isle Royale fur- 
nishes this mineral in greater amount than any equal area in 
Minnesota. It occurs at the Island Mine, at Chippewa Har- 
bor, at Scovill's point and at two miles SW from Locke's 
point, on the north side of the island. On the north shore of 
the lake, in Minnesota, it has been detected at Terrace point 
(near Grand Marais), at Fall river where it can be seen to be 
a product of alteration of labradorite (200 A), at Poplar river 
and eastward, east of Pork bay (163 A) and at Beaver bay. 
At the last point it forms the chief constituent in veins in the 
anorthosyte masses at the west point of the bay. It occurs 
in the rock of Encampment island. 
Lintonitc. Associated with mesolite and thomsonite at 
Terrace point are occasional light green, apparently amor- 
phous, small round pebbles, usually found in best form in the 
debris of the beach. These are also in the rock that contains 
the mesolite masses, and often the two can be seen in the same 
cavity. Indeed they are very intimately associated, and the 
green color of some of the most prized pebbles is due to this 
substance. It forms bands of color, and it fills triangular areas 
between the radiated forms of the spherulit.es when several 
spherulites are crowded together in one mass. It has a green 
glassy translucency, and its hardness is about that of mesolite. 
This mineral was analyzed by Miss Laura Linton and re- 
ported by Peckham & Hall with the following result, (i). 
Analysis (2) is by F. L. Sperry. 
(I) (2) 
SiOg 40.21 44.53 
AI2O3 30.21 27.36 
CaO 10.37 9-90 
NagO 4-o6 5.92 
K2O 0.49 MgO 0.26 
H2O 1375 13-08 
FeO - 0.40 
99.89 101.05 
It was considered by them as a form of the same mineral 
(mesolite) and was classed by Dana with thomsonite, to which 
all of these Terrace point zeolites were referred. 
