

CRETACEOUS AND TERTIARY—GENERAL ARRANGEMENT. 141 
which he correlates with groups 1, and 2. Group D. is described as 
consisting of “sandstone overlying marly clays, banded with thin seams 
of ironstone, thin beds of limestone, stiff dark blue clay, and arenaceous 
shales, with Ostrea cortex, O. vellicata, O. anomiceformis, Cytherea, Mytilus, 
Cardium, Venus, Natica, &c., and stems and roots of silicified trees.” * 
Rocks of this series, he believes, underlie a considerable area of the third 
great prairie plateau, and are mentioned as occurring on the lower part of 
the Red Deer River, at the Hand Hills, at the Elbow of Battle River, above 
Fort Pitt on the North Saskatchewan, on the Bow, and Belly Rivers, and 
also to the west and north of Edmonton. The relations of this group 
with those above and below it, do not seem, however, to have been very 
clearly made out, and Dr. Hector appears to remain in some doubt, as to 
its position and distribution.¢ Ostrea vellicata, and O. anomiceformis, are 
shells characteristic of the Cretaceous formation, in its development near 
the Mexican frontier, and while their occurrence probably places beyond 
dottbt, the Cretaceous age of some of the beds here referred to, it is 
probable that others, especially in the more southern localities, may 
belong to the marine base of the Tertiary; the rocks of which, in some 
places near the forty-ninth parallel, answer closely to their description. 
Cretaceous No. 3.— Niobrara Group. 
345. The occurrence of rocks of the Niobrara, or 3rd division of the 
Cretaceous, in the escarpment ot Pembina Mountain, near the Boyne River, 
has been already noticed. (p.78.) The specimens, so far as they go, ex- 
actly resemble those of this member in the typical section in Nebraska, 
which Dr. Hayden thus describes :—“ Lead-grey calcareous marl, weather- 
ing to a yellowish and whitish chalky appearance above, containing large 
scales and other remains of fishes, and numerous fragments of Ostrea conjesta 
attached to fragments of Inoceramus, passing down into light-yellowish 
and whitish limestone ” and blending with the next lowest group. ‘“ At 
the Black Hills this rock sometimes presents its normal appearance, but 
generally there, as well as along the Rocky Mountains further west, is 
scarcely distinguishable lithologically from the formation below.” t In 
Colorado, according to Mr. Marvine, No. 3 still retains to some extent 
its calcareous character, and consists in great part of impure limestones, 
often highly fossiliferous. § | 
* Exploration of British North America, p. 227. t Ibid., p. 229, 
t Geological Report Yellowstone and Missouri Expedition, p. 14, 
§ U. 8, Geol. Surv. Territ., 1873. p. 102. 

