112 B. N. A. BOUNDARY GOMMISSION. 
Tertiary plateau, however, throws doubt on Dr. Hector’s supposition of 
the continuity of the edge of the Tertiary between the two last mentioned 
localities. Judging from anvoiogy, there is reason to believe that the 
bay of Cretaceous rocks must extend continuously from the north side of © 
the plateau to the South Saskatchewan River. The strata are as nearly 
as possible horizontal, and throughout this region it is found that a valley © 
once cut down through the harder Tertiary rocks to the Cretaceous, does 
not in the lower part of its course again pass over the former. Dr. Hector 
did not reach the northern edge of the Tertiary between the Cypress and 
Thunder Breeding Hills, and it is by no means certain that there is a 
continuous escarpment uniting them, as shown on the map. 
274. Twelve miles east of the White Mud River, in the banks of a 
deep coulée tributary to it, good exposures of the Cretaceous rocks occur, 
and yield in great abundance the characteristic fossils of Meek and 
Hayden’s 4th group. Baculites compressus is the most common form, 
and is associated with several species of Jnoceramus and other molluscs. 
Specimens of Avicula (Pteria) linguiformis M. and Acteon concinnus, M. 
& H., are included in the collection, and are especially interesting, as. 
having been previously recognised by Prof. Hind, in localities further to 
the north,—the former at the elbow of the South Saskatchewan, the 
latter at Two Creeks on the Assineboine. 
275. The fossils resemble very closely, both in their general appear- 
ance and mode of preservation, those brought by Dr. Hayden’s expeditions 
from the Upper Missouri. They are included in nodules of ferruginous 
limestone, which, like the enclosing clays, are of dark-grey colour. 
The concretions only occur in certain beds of the clay, and are generally 
more or less septarian in character, the cracks being filled with amber- 
coloured calcite. In other parts of the section, beds with large ironstone 
concretions occur, which usually have the same septarian character, but 
were not observed to contain many fossils. Selenite crystals abound in 
the clays, and a fibrous mineral, which may best be called a ferro-calcite, 
occurs in discontinuous layers parallel to the stratification ; one of which 
was observed to be nearly a foot in thickness. This substance was also 
found in connection with the sombre clays of the Wood Mountain 
Astronomical Station exposures, and with those of the Bad Lands. 
($ 258-263.) It is minutely prismatic, the prisms in some cases, radi- 
ating from a centre, but more usually nearly parallel, and at right angles 
to the beds. It is pearly-grey within, but weathers yellowish-grey, and 
in that state much resembles, at first sight, silicified wood. 

