
” 

CRETACEOUS AND TERTIARY—THREE BUTTES. 127 
similar position on the East Butte, and probably indicate the base of 
division 4, and the top of the next lowest division of the Cretaceous. 
They might very well represent the sandstones which apparently under- 
lie the dark clay-shales near the Hast Fork of Milk River. Overlying 
No. 4, are massive sandstone beds, yellow in colour, and though in this 
place much more uniformly indurated, than those seen in the same 
relative position further east, no doubt represent the Upper Cretaceous 
sandstones of Division y., of the Bad Land sections. These sandstones, 
from their superior hardness, generally form a prominent ridge, at a 
little distance from the base of the Butte; some layers are flaggy and 
thin-bedded, but they did not appear to contain any fossils. On the west 
flank of the Butte, they dip away at an angle of about 12°, and a thick- 
ness of over forty feet is exposed. 
312. The exhibition of the lower rocks at the Buttes, enables the 
relative position of those forming the surface of the country—and traced 
almost continuously from Milk River to this point—which might other- 
wise have been a doubtful question, to be definitely ascertained. They 
are found to overlie the upper Cretaceous beds, and to be related to them - 
precisely as the lowest beds of the Lignite Tertiary are, in the Bad 
Lands south of Wood Mountain. The character of the Cretaceous beds 
is little changed, though the tendency of No. 4 seems to be, to become 
somewhat coarser in this direction. The Lignite Tertiary rocks have, 
however, changed very materially, and especially in becoming more 
distinctly marine, and perhaps also less lignitiferous. 
313. With regard to the age of the igneous masses, here so unex- 
pectedly found, all that the sections prove, is that they are later than the 
Lignite Tertiary rocks, which are elevated by them and traversed by 
their dykes. They are probably protrusions quite local in character, 
and not broadly based on similar rocks. This is indicated not only by 
the comparatively very slight metamorphism which the surrounding 
beds have sustained, but by the very rapid increase of the dip on 
approaching the masses, and the short distance which the disturbance 
consequent on their protrusion is found to extend. They have not, 
however, at all the character of modern volcanic cones, and I did not 
see any rocks in connection with them which had even probably cooled 
at the surface. If of the nature of volcanoes they are very ancient 
ones, of which the cores, or stumps, now only remain, and from about 
which the whole of the ejected material has been removed. The denu- 
dation affecting the rocks tilted up round the Buttes has been very great, 

