i 
aD, ‘ 
z wien 7 
, og 
126 B. N. A. BOUNDARY COMMISSION. 
peaks and ridges rise, and enclose a rugged, pine-clad, and rocky area of 
some extent. The foot-hills of the western Butte are also on a larger 
scale than those of the others, and an examination of their rocks served 
to explain much formerly in doubt. The sedimentary rocks are here, as 
at the east Butte, found to dip away from the central igneous intrusion on 
all sides; but a considerable mass of stratified rock, has here been, as it 
were, caught up by the eruptive material, and occupies the depressed 
central portion of the group of mountains. A great part of these beds 
dip south-eastward at a rather high angle; they have been very consider- 
ably altered, and consist now of slaty shales, and hard, thin-bedded 
sandstones, in which I was unable to find any fossils by which their age 
might be made certain. I have little doubt, -however, that they are 
Cretaceous. The trappean nucleus of this Butte is indistinguishable, 
lithologically, from that of the East Butte, formerly described, and forms 
shattered and rubbly hill-tops, in the same way. 
310. The clearest sections of the rocks surrounding this Butte, were 
met with on its western side, (Plate VIII., Fig. 2.) where a considerable 
brook issues from the central valley. The shaly-clays of division 4 of the 
Cretaceous, are here seen with a gentle westerly dip, somewhat indur- 
aled, and in places, baked into rather hard black clay-shale, corresponding 
exactly-with that previously found surrounding the East Butte. Their 
thickness, as developed here, may be roughly estimated at about 800 feet, 
though the nature‘of the sections did not allow of precise measurements. 
They are not here found to be characterized by the same abundance of 
septarian nodules, as in localities east of Milk River; a few such, 
however, occur, and minor arenaceous layers are also intercalated, and 
sometimes found to persist a considerable distance horizontally, though 
generally quite local and lenticular. In one of these masses a number of 
fossils were found, which though not in a very good state of preserva- 
tion, are very interesting. They include one or two species of 
Inoceramus, several gasteropods resembling Fusus, fragments of an. 
Ammonite, and a portion of a Belemniteila, probably B. Bulbosa, M. & H. 
Some fish scales, found with the other fossils here, are specifically 
identical with some of those occurring in certain beds at Pembina 
Escarpment, 600 miles distant, (Plate XVIII, Fig. 1.) and were not 
observed in any intermediate locality. 
311. Underlying these clay-shales of No. 4, in some places, are 
rather massive sandstones, tilted at high angles against the flanks of the 
eruptive rock. They represent the sandstone beds found occupying a 
