THE NORTHERN PACIFIC ROUTE, 117 
At Trident, in the canyon of the Missouri, there is a large plant 
for the manufacture of cement from the Threeforks (Devonian) shale, 
ae which is obtained from the crushed rock in the over- 
o turned anticline shown in the diagram. From Three- 
pace Aisadere, forks to Lombard, a distance of 15 miles, the Chicago, 
+ aA) eS. . 
Milwaukee & St. Paul Railway parallels the Northern 
Pacific, on the opposite side of the river. 
lan 
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rad m ’ ie 
“ aoe” a ‘ lag 
$ 0% 0) a apt ees ce a; elle eee 
0 oy ¢ pee i a %. i 
7 
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Figure 26.—Faulted fold at Trident, Mont., lookiag northeast. 
For 5 miles beyond Trident the railway winds in and out on the 
flanks of the anticline, making a long cut in the Madison limestone at 
the sharp bend of the river. From this point the river turns back 
toward the southeast, cutting down through the formations, until it 
reaches the Belt series—the lowest in the section. Beyond this point 
the soft material of the lake beds obscures the hard rocks, and the 
hills formed by those rocks recede a mile or more from the river. 
The valley on the right (east) is wide and the hills are low as far as 
Clarkston siding, but on the opposite side of the river and rudely 
parallel with it there is a mountainous ridge, formed 
Glarkston. by the overturned northwest side of a syncline which 
— papier lies parallel with the general course of the road and 
‘Paul 1,071 miles. nich is shown in figure 25. The southeast side of 
this fold is obscured by the lake beds, which cover all older forma- 
1'The mill at Trident has a daily ca- | Rockis taken from all parts of the cut and 
pacity of 1,600 to 1,800 barrels of cement then mixed until the proper —- 
and is modern in all its equipment, hav- | of the constituents are proc or the 
ing been erected in 1910. Material m manufacture of cement. The raw mate- 
cement contains approximately 75 per with Red Lodge coal as a fuel. (For a 
cent carbonate of lime, 15 per cent silica, description of Red e see 
and 5 to 7 per cent alumina and iron | note on p. 82.) Th 
oxides, with very little magnesia and no | 95 per cent of it will pass 
sulphur, This combination is found in | mesh sieve, i 
the Threeforks (Devonian) shale, which | of the revolving cylinders. It burns like 
is quarried extensively along the east | gas, producing @ temperature of about 
3,000° F. The burned cement is crushed 
siderably in composition, that from the | and mixed with a little gypsum to regu 
upper end of the cut being very limy and | late the setting t y for 
that from the | d earthy and sandy. | the market. 
