124 B. N. A. BOUNDARY COMMISSION. 
smaller than the others. It has, however, an exceedingly symmetrical 
conical form, as viewed from almost every direction, and its slopes must 
form an angle of nearly 45° with the horizon. Like the Kast and West 
Buttes, it is surrounded by grassy foot-hills, which are specially promi- 
nent on its northern slope. 
305. Dykes of eruptive material, traverse the sedimentary rocks 
surrounding the Buttes, in some places, and appear generally to have a 
direction radiant from their higher peaks. In a valley about ten miles 
north of the summit of the East Butte, one of these is well exposed. By 
the wearing away of the softer surrounding beds, it stands up like a 
massive partly-ruined wall, the resemblance being increased by the fact, 
that the rock has been broken up by the weather, into quadrangular 
blocks. Its observed course is N. 70° E. (mag.) The rock would pro- 
bably be included under the name Kersanton, of Von Cotta’s classifi- 
cation, and is a mica-trap of dark greenish-grey colour, and not very 
hard; in which small tabular crystals of brown mica are thickly 
disseminated. It has probably been originally of the same nature as the 
acidic central masses of the Buttes, but has become more basic by the 
incorporation of portions’ of the surrounding sedimentary rock; and has 
acquired a different mineralogical character, from this circumstance, and 
its more rapid cooling. The clays and sandstones on either side, are nearly 
horizontal, except immediately in contact with the dyke, where they are 
bent and contorted, and much altered. Some dark carbonaceous shales, 
especially, are so much hardened, as to bear a close resemblance to those 
usually found associated with coal beds in the Carboniferous formation. 
valves of Ostrea, are abundant in some of the surrounding beds, and 
specimens of Corbula undifera were also recognised. 
306. On ascending the East Butte, the harder beds are found consti- 
tuting more or less continuous ridges, round the central masses, while 
the softer intervening strata are not usually well exposed. The total 
thickness of the beds seen is not very great, as the ground rises almost 
equally with the increasing dip. There are, no doubt, also many small 
dislocations which complicate the ,section. The sedimentary rocks, in 
some places, rise to within about one thousand feet of the summit, and 
are then found much hardened and altered, and dipping very steeply 
away from it. They are here also traversed, like the igneous rock itself, 
by many small seams of crystalline quartz, in which a careful examina- 
tion failed to detect a trace of any metallic mineral. As some of these 
veins appeared, however, to be not without promise, I afterwards panned 

