THE NORTHERN PACIFIC ROUTE, 91 
opposite the mouth of Mill Creek, to leave the terrace and descend 
to the valley bottom on which lay the great mass of ice. 
In the vicinity of Emigrant there is a thin sheet of basalt (a dark 
massive volcanic rock) capping the terrace on the right. This rock 
exhibits the vertical columnar structure common to 
Emigrant, such material, and it is probable that the several 
Elevation 4887 feet. masses of basalt which can be seen up the canyon are 
St. Paul 1,031 miles. As ; 
parts of one lava flow that originated somewhere in 
the park and extended down the valley as far as this place. It can 
be followed on the right for 3 miles, but beyond that it has been eroded 
for some distance, leaving no trace of its presence. 
In the vicinity of Emigrant the most prominent topographic fea- 
ture is Emigrant Peak (Pl. XIV), which dominates the entire valley. 
From the train this appears to be an isolated mountain, but the map 
shows that it is merely a prominent spur projecting from the moun- 
tain mass. The peak has an altitude of 10,960 feet, and its summit 
stands 6,000 feet above the valley. The base of the peak is composed 
of old gneiss, a rock which the traveler will have a good chance to 
see at close range farther up the canyon, and its summit of the 
andesitic breccia and lava flows that at one time probably almost 
engulfed the range on the east and completely submerged that on the 
west. At milepost 24 the high, sharp summits of the Gallatin Range 
show on the right (west), but they are neither so rugged nor so im- 
posing as the peaks on the east. ; 
The sheet of basalt capping the terrace on the right in the vicinity 
of Emigrant disappears for a mile or more, but opposite milepost 28 
it reappears on the other side of the river, capping a finely developed 
terrace at a height of about 150 feet above the river. 
At Daileys, a little farther on, a complete section of the rocks 
forming the terrace can be seen, and these rocks record an entirely © 
new chapter in the geologic history of this region. 
Daileys. They consist of white marl and conglomerate over- 
Elevation 4,941 feet. Jain by dark gravel and the whole covered with the 
St. Paul 1,039 miles. . ; 
sheet of basalt that was poured out upon the surface 
as molten lava. The white materials are known, from their compo- 
sition and the fossils they contain, to have been deposited in a lake 
or lakes in Miocene or Pliocene time. A brief description of these 
lake beds is given on page 113. 
The sheet of basalt capping the terrace can be followed as far as 
milepost 33, but from that point nearly to the entrance to the park 
the terrace and the basalt are not present. At Point of Rocks, only 
a short distance farther on, the traveler can obtain a good idea of the 
kind of material composing a volcanic breccia, for the railway cuts 
through a projecting point of the breccia and it can be seen at close 
