THE 
AMERICAN NATURALIST. 
VoL. xu.— FEBRUARY, 1878. — No. 2. 
ON THE N RECENTLY eo ea IN THE 
AKOTA BEDS OF COLORAD 
BY E. D. COPE.- 
i las formation known as the Dakota was long since characterized 
by Messrs. Meek and Hayden, from the studies made by the 
latter gentleman, of the great section exhibited by the Missouri 
river. Subsequently Dr. Hayden, then as now, the esteemed di- 
~ rector of the United States Geological Survey of the territories, ob- 
= served and defined the same horizon along the eastern flank of 
_ the Rocky mountains. Doctor J. S. Newberry, in his reports on 
: the. geology of the Colorado basin, has mentioned the same 
_ stratum under the name of Lower Cretaceous sandstone, and I 
~ have in my report to Lieut. Geo. M. Wheeler identified that part 
J of these sandstones which is seen in northwestern New Mexico, 
2 with the Dakota. This formation is then one of great extent 
_ and importance. It consists chiefly of sandstones which are 
sometimes so amorphous as to constitute a quartzite. Among 
| _ these are interstratified beds of clay, carbonaceous clay, and lig- 
_ nite, some of which may be used as an inferior fuel. These 
: _ mineral characters show that the formation was, as pointed out 
_ by Prof. Newberry, deposited in shallow water during a 
_ period of subsidence. He remarks that previous to this subsi- 
_ dence there was an extensive land area ; but that it steadily dimin- 
_ ished by the encroachments of the ocean. This period of ex- 
_ tended dry land, would be regarded by many geologists as a part 
_ of the great cretaceous division of time; that occupied in its 
_ sinking, and in the deposit of new pete being now paral- 
_ lelized with the later half of the cretaceous period of the old 
world scale. In any case the deposit of the sands which became 
the Dakota rocks, marks the beginning of the cretaceous ocean 
in North America, and is the No. 1 of Meek and Hayden. - 
VOL, XII.—NO. II 
