io8 The American Geologist. February, i905 
The company operating this mill, or the "Montana 
Aluminum Plaster Co." manufactures five different products 
from the raw gypsum — stucco, plaster of Paris, aluminum 
hard finish plaster, sand plaster and calcimine of various 
colors. The annual product from this plant is about i,8oo 
tons. 
Tlie mill and mines are lighted with electricity, gener- 
ated by means of a small dynamo at one end of the mill. 
The mill at present is run by steam but the company expects 
to dam Belt creek within another year and thus run on a 
more economical basis. The mill is within twenty yards of 
the railroad, thirty yards of the creek and fifty yards of the 
mines. Everything is ideal for a plant of this sort. 
The Gypsum Beds. 
Tlie beds found here are between twenty-five and thirty 
feet thick, and extend over an immense area. They are 
nearly horizontal, having a slight dip to the northwest. The 
gypsum itself is quite pure (see analyses) but is interstrati- 
fied somewhat in places with considerable clay. 
The gypsum is not more than from lOO to 300 feet be- 
low the surface and is capped by and rests upon a hard 
compact limestone ; several fossils were gathered from the 
rock above and sent to the U. S. National Museum for 
specific identification and the horizon was pronounced 
Jurassic. 
From the dip, geological formation, and other indica- 
tions the beds here are pronounced the same as at Kibby, 
nine miles away. If this be true the field at this place has 
by far the largest productive area of any in the state. The 
beds thin out to a few feet at Kibby and most of the mate- 
rial worked there was exposed. 
The other bed that belongs to this, or the middle field, 
is located in the Big Snowy mountains, near Portuguese, 
about thirty-five miles south of Lewiston, Fergus county. 
Tlie material is of a very good quality and it is claimed that 
an immense ledge is exposed. No development of any con- 
sequence has ever been done here ; but since the railroad 
now passes within a few miles of the deposits, good use is 
expected soon to be made of them. 
