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CRETACEOUS AND TERTIARY—NEAR WEST BUTTE. 129 
By could find no rocks older than those of the Upper Cretaceous in 
, connection with the mountains, and the plain appears to be based 
entirely on the Lignite Tertiary beds. 
Cretaceous and Tertiary Rocks from the West Butte to the Eastern base of 
the Rocky Mountains. 
316. Westward from the West Butte, the beds are found to assume 
* a gentle synclinal form, and exposures are not infrequent in the steep 
banks of coulées. About six miles from the base of the West Butte, a 
gone of sandstone appears, which must hold a position considerably 
: above the base of the Lignite Tertiary, as the beds are still dipping 
westward at low angles. Two miles further west, the same sandstones 
are again seen, but now with a gentle eastward dip. The eastern and 
western outcrops of the sandstone form the low -escarpments of a 
plateau, due to its superior hardness, which occupies the trough of 
the synclinal. (Plate VIII, Fig. 2.) This synclinal arrangement is 
not, however, persistent, nor of great structural importance, as, in 
proceeding westward, sandstones which appear to occupy the same 
horizon in the Tertiary, are soon again found nearly horizontal. 
317. In asystem of ravines south of the Line, about twenty miles 
west of the base of the Butte, these sandstones are again well exposed, 
and have an estimated thickness of over thirty feet. In these valleys 
they occur not much below the general level of the prairie, and forming 
the upper parts of the banks, give them a most picturesque and remark- 
ie ee ee Lee ed | =a =Oos ¥ 
able appearance. The lower layers of the sandstone are generally very 
regularly bedded, and some of them are exceedingly fine and thin, and 
show worm-tracks and other obscure markings. The upper beds are 
more massive and have a nodular character, which causes them to 
weather out into the castellated forms, resembling in some places those 
of the Roche Percée. (Plate VIII., Fig. 1.) Underlying the sandstones 
are less permeable clays, or arenaceous clays, of light colours, of which 
I did not succeed in finding good exposures, but which turn out 
numerous small springs of a highly saline character. The beds appear 
to be quite horizontal in this locality. 
318. Near this place, and about ten miles south of the Boundary- 
line, a bold escarpment occurs, facing southward, toward a great stretch 
of lower country. Its outline is that of any section of the bank in the 
last described valley, its abrupt edge being produced by the sandstone 
zone in the same way. From the rapid falling away of the surface of 
9D 
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