THE NORTHERN PACIFIC ROUTE, 53 
formation), partly of marine origin, and represent the bottom of the 
sea that through later Cretaceous and part of Tertiary time covered 
the region.! 
The railway follows Heart River for some distance and then turns 
to the right and climbs to the upland along Sweetbriar Creek. Here 
large bowlders of granite and other similar rocks may 
Judson. be seen on both sides of the track. These are par- 
aa —— eter ticularly numerous and very large, some as much as 
; 8 feet in diameter, in the vicinity of Judson, but scat- 
tered bowlders can be seen from the car window beyond New Salem. 
Rocks of this kind are not known to crop out in the State, so it is sup- 
posed that the bowlders must have been brought here by ice, but as 
1The rocks exposed along Missouri 
River from the vicinity of old Fort Pierre 
in South Dakota to and beyond the cross- 
ing of the Northern Pacific Railway at 
Bismarck dip slightly to the north or 
northwest and are encountered in go- 
ing up the stream in ascending order. 
First i is the Pierre shale, which consists of 
ag dark shale that carries 
marine shells wherever it has been found 
from the Canadian line to New Mexico. 
It was doubtless laid down when the en- 
tire Rocky Mountain and Great Plains 
regions were sunk below the level of the 
ocean. 
This formation is overlain by a coarse, 
generally clean white or brownish sand- 
stone, called Fox Hills, which was evi- 
dently at one time the sandy shore that 
followed the retreat of the Pierre sea. 
Sandstone as a rule is not good material 
for the preservation of fossils, but here and 
there the Fox Hills sandstone 
has been regarded as the last formation in 
The Fox Hills sandstone is followed by 
the Lance formation, which consists of 
sandstone, shale, and coal beds. Few 
shells occur in the Lance, but those that 
shave been found in the larger part of the 
) and of fossil leaves and 
trunks of trees in the sandstone and shale 
shows clearly that the Lance formation 
accumulated above sea level as material 
either brought down by streams and 
spread out over the even surface of the 
land or deposited in lakes. This for- 
mation’ covers much of the mountain 
and plains country north of Colorado, 
and in most of this broad area it con- 
tains nothing but fresh-water material. 
Recently, however, marine and brack- 
ish-water shells have been found in the 
upper part of the Lance in south-cen- 
tral North Dakota and also along Little 
Missouri River in the southwest corner of 
the State, which indicate that after the 
recession of the sea to the east at the close 
of Fox Hills time it reappeared and 
reached as far west as the Montana line. 
Then at the close of Lance time the sea 
again disappeared from this region, never 
to return, as all succeeding formations are 
_ of fresh-water origin. 
For many years the age of the Lance 
formation has been in dispute. The fossil 
shells and the great dinosaurs (see p. 73) 
indicate that the formation is Cretaceous 
those of the overlying Fort Union forma- 
tion. Although the question is not 
finally settled, it seems probable that the 
Cannonball member of the Lance forma- 
tion is Tertiary and that the Cretaceous 
fauna which occurs in it i is merely ® sur- 
which parce lived in the open sea but 
whi 
land preserved its old form even into Ter- 
tiary time 
