122 Peckham and Hall—Thomsonite from Minnesota. 
clusion that, in pre-Primordial times, the petro-siliceous rocks, 
to a considerable depth, were changed by the action of atmos- 
pheric agents, not to kaolin, as generally at the present time, 
but to or toward pinite ; and that subsequently this decompo- 
sition-product was, for the most part, swept away by the sea in 
which were deposited the teroetha and the Primordial conglom- 
erate. 
h the northwest shore of the Nook. visible only 
at low tide, is a hard, oo compact, feldspathic sandstone 
or slate, the age of which is unknown. It rests unconforma- 
bly Vee the banded petiocilés forming the shore at this point; 
and the layer of pebbles at its base shows very clearly that the 
sandstone is chiefly composed of the débris of the petrosilex. 
This origin explains the highly feldspathic nature of the sand- 
stone. Scattered through the sandstone are clear, almost trans- 
parent, rhombic crystals of orthoclase, 3 to 6™ long, which are 
very clearly indigenous in their present positions. Occasion- 
ally they are sufficiently numerous to give a porphyritic aspect 
to the rock. LErratics of this sandstone are scattered all over 
the Neck; and in some of these which are very thoroughly 
icant the orthoclase crystals are changed to a soft, unctu- 
ous, waxy, green mineral,—in other words, to pinite. Where 
the southern has been less thorough, the characters of the 
pinite are less strongly marked. 
stiabiniienhaeoeint 
Art. XV.—On Lintonite and other forms of Thomsonite: A pre- 
liminary notice of the Zeolites es the vicinity of Grand Marais, 
County, Minnesota; by S. F. Prcknam and C. W. 
Hatt. 
GRAND Marais is situated on the northwest coast of Lake 
Superior, one hundred and eight miles northeast of Duluth. It 
is the site of an early French trading or mission station, and 
was inter a station of the Hudson Bay Company. Its beauti- 
ful land-locked bay furnishes the only good harbor between 
Duluth and Pigeon Point. 
The rocks, for several miles east and west, as well as at the 
Marais, are classed in general as igneous, and have often a basal- 
tic structure. They present, however, great diversities of charac 
ter both to the chemist and lithologist ; and while the mineral 
He are perhaps altogether old, the forms are in some cases 
was our original intention to confine this research to 
a or two peculiar forms that first attracted our attention, but 
in the progress of our examination the subject has outgrown its 
