io6 The American Geologist. February, i905 
Anhydrite gypsum crystals are found 14 miles west of 
Wibaux, Montana, in the "bad lands" of (ilendive creek, 
Dawson county. The butte on which the crystals are found 
is one of the highest in this region, and is capped by a 
scoriaceous volcanic rock. The crystals are found about 30 
feet below in a "gumbo" clay. The transition of selenite to 
anhydrite is beautifully shown. The heat of the overlying 
lava thus caused the change. The crystals are found in the 
Laramie and are the only native anhydrite crystals so far 
known in Montana. 
The middle and southern beds are the only ones being 
worked at present, and only one mill is being operated at 
-each place. 
The Middle Field. 
The principal beds now being worked in this field are 
located in the northwestern part of Cascade county and cover 
quite a large area. According to Weed "the series of beds 
may be traced from the Missouri river eastwards along the 
flanks of the Big Belt mountains to Riceville on the Neihart 
"branch of the Great Northern railway ; thence eastward to 
the town of Kibby, and thence around the flank of the Little 
Belt mountains in a nearly continuous exposure to the vicin- 
ity of Castle mountains. Southward from that locality the 
same horizon can be traced by its red shales, but the gypsum 
does not occur, so far as known, in sufficient purity or thick- 
ness to promise commercial importanbe." 
This field was visited during the past summer and found 
to be in a flourishing condition. Mr. A. J. Voight, the pres- 
ent president and manager of the only stucco and plaster of 
Paris mill in this field, made it possible for the writer to in- 
vestigate the beds and mill and closely examine the products. 
Mr. Voight formerly owned and managed the Kibby plant, 
but after this latter burned, the beds nine* miles northwest 
of Kibby and six miles above Armington were opened and 
in 1900 the new or present plant was installed. "The mill 
of this plant is located directly on the Neihart branch of the 
Montana Central railway six miles above Armington, on 
Belt creek and thirty-four miles from Great Falls. The mine 
is directly back of it and sufficiently high on the hillside so 
that gravity is largely helpful in handling the rock." Some- 
