
58 B. N. A. BOUNDARY COMMISSION. 
alternate in broad belts, according with the stratification. The bedding 
is very regular, and is marked, besides the alternation of tint, by the 
erosion of some softer layers composed of thin flaggy beds, which 
alternate with massive compact layers several feet in thickness. The 
fracture of the more massive portions is conchoidal, with a dim lustre, 
and the colours of freshly broken surfaces are much less marked than 
those of the exterior, and vary from light grey, to dull purplish and flesh- 
colour, some beds being a pale pink. 
118. The structure of the rock is generally very close and fine, and 
from the preponderance of sedimentary matter, it frequently more re- 
sembles a metamorphosed mud-rock, than a true dolomite. It does not 
effervesce in cold dilute acid, but on heating gently, a brisk action 
commences ; and when the whole of the magnesian and calcareous matter 
has been removed, a coherent, though brittle mass, remains. This, when 
examined microscopically, is found to consist of very fine and uniform 
argillaceous and silicious particles. The exposed surfaces are generally 
decomposed to a depth of afew lines. Small grains of iron pyrites are 
sometimes included in the rock, but no organic forms of any kind were 
discovered. 
119. Of these rocks, at least seven hundred feet in thickness is 
exposed ; they are well shown at the Cascade on the western shore of the 
lake, but to the south soon dip out of sight, and overlying beds come 
down to the water level. The southern end of Waterton Lake, 
I was, however, unable to examine in any detail, from the precipitous 
and impassible nature of the mountains surrounding it, and the impossi- 
bility, in the short time at our disposal, of making a servicable boat or 
raft. . 
120. Resting directly on these peculiar dolomites, is a very massive 
bed of limestone, also dolomitic, which forms a prominent feature from 
the chalky-white aspect of its weathered surfaces. It may be designated 
by the letter B., and has a probable thickness of about two hundred 
feet, and includes at least one well-marked band of coarse magnesian 
grit. The limestone on fresh fracture is of a pale-grey colour, and has a 
highly metamorphic aspect. It is very close-grained and compact, and 
breaks with a splintery fracture, the original planes of deposition being 
almost entirely lost. Some layers are exceedingly cherty, the siliceous 
matter being at times aggregated into well-defined nodules, but more 
usually disseminated, and forming an irregular skeleton, which gives 
to some weathered surfaces of the limestone an exceedingly rough 
