THE NORTHERN PACIFIC ROUTE. 125 
West of the summit the rock is not well exposed, partly for the 
reason that it is shale (Cretaceous) which is not hard enough to form 
ridges or knobs. This shale is the youngest rock crossed by the rail- 
way in this vicinity. It lies in the middle of the great syncline pre- 
viously referred to and constitutes the core of the fold. West of 
this place the rocks should be crossed in reverse order, but they are 
so badly faulted and cut by intrusive masses that it is very difficult 
_ to determine the structure. The most prominent rock on this side 
of the fold is the Madison limestone which is quarried at Calcium, 
between mileposts 26 and 27, and burned into lime. 
West of Calcium the rocks are badly broken by faults so that it 
is almost impossible to identify the various formations from the 
moving train, but near milepost 28 there is a prominent ledge of 
quartzite (Quadrant) on the right (north) which carries at its top a 
valuable bed of rock phosphate. Analysis shows this rock to contain 
from 40 to 60 per cent of phosphate of lime. This material is valuable 
as a fertilizer, and the United States Geological Survey has been 
actively engaged in the last few years in mapping deposits of such 
rock. It is described by R. W. Stone below.’ 
cha 
on the Pacific coast and 
who paedaae ‘came i into prominence in 
the Civil War, and Lieut. John Mullan, 
who was in charge of an exploring party 
in the Rocky Mountains and who later 
achieved local distinction through the 
building of a military road from Fort 
Benton to Walla Walla. (See p. 131.) 
Late in the summer of 1853 Lieut. 
Musselshell River by way of the Judith 
Basin. He tried to induce some Indians 
to guide him through a low pass that had 
been reported west of the place where 
Helena now stands, but the Indians were 
on a hunting trip for their winter supply 
of meat and could not be induced to join 
him. Failing in this, he ascended the 
Musselshell cy crossed the Big Belt 
Mountains to the site of Helena. He 
Pass. Twenty years later the same route 
was followed by the locating engineers of 
the Northern Pacific and the original line 
is over 5 feet thic 
61.6 per cent of tricalcic phosphate. De- 
tailed examination has shown that within 
mining depth approximately 86 
tons of rock phosphate, or an equivalent 
of 5,440 acres underlain by a bed 4 feet 
thick. The phosphate is in a definite 
or rocks, 
as ‘coal i is. At Elliston the eal bed 
is nearer the railway than elsewhere in 
western Montana. Phosphate is found in 
the same formation in the hills 5 miles 
north of Garrison; near Philipsburg, a 
town at the end of the branch south of 
Drummond; at Lime Spur; and at Mel- 
rose, 30 miles south of Butte. 
When rock phosphate was discovered in 
graphic “— and quantity of available 
material. It has been found that rock 
Paap occurs in the mountains of 
Montana, Idaho, Wyoming, and Utah, 
in quantities so stupendous that when 
e in tons the amount is — 
inconceivable. The — 
e areas e€ hey 
1913 is a as! 7,777,000,000 long 
