176 TJie American Geologist. March, isso 
is believed to be remote. Until, however, the counties to the 
north arcstudied in more detail than has so far been possible, 
the absence of such later drift can not be positively afifirmed. 
It may be said, however, that so far no extra-morainic drift 
is known as far north as Carroll county which is not known 
to be Kansan or might not readily be assigned to that forma- 
tion. 
[Contributions to tlie Mineralogy of Minnesota. V.] 
COMIVION ZEOLITES OF THE MINNESOTA 
SHORE OF LAKE SUPERIOR. 
By N. H. WiNCHELL, Minneapolis, Minn. 
Stilbitc. This zeolite is sometimes confounded in the field 
with heulandite. It is easily cleavable parallel to 010 and 
presents a shining or nacreous surface which often gives an 
iridescent reflection. Its color is white, when pure, but its 
most frequent color includes some shade of red, or orange red. 
due to the presence of more or less hematite intercalated in the 
cleavages and other openings. The optic plane is parallel 
with the cleavage (010), and hence a cleavage piece will show 
the emergence of /^m. a character which at once distinguishes 
it from heulandite. 
Localities. Occurs at Splitrock point; Beaver bay; Lit- 
tle Marais; at three miles east of the mouth of Poplar river, 
where it affords large cleavable plates so twinned as to form 
more or less radiated and fan-shaped surfaces; mouth of False 
Poplar river: also near the mouth of Temperance river. Stil- 
bite is frequently seen in company with heulandite. 
Heulandite. Is usually red, frequently forms a coating in 
joint-planes in the basic rocks. Its cleavages show an axis 
of elasticity (//g) in the acute angle of the optic plane. In the 
field its simpler cleavage and plates (i. e. untwinned) afford the 
best means of distinguishing this mineral from stilbite which 
is usually so twinned as to present its edges in diverse and mul- 
tiple directions in the same mass. Heulandite is also more 
liable to show a cherry red stain of hematite. Under the mi- 
croscope a single small cleavage fragment at once distin- 
guishes it from stilbite. since in place of //„! it shows the bi- 
sectrix n„. 
