832 “STRATIGRAPHICAL GEOLOGY. — [Boo VI. 
its presence is recorded chiefly by limestones, among which oceur abun- 
dant hippurites (Caprotina, Caprina) and foraminifera (Orbitolites). 
Northwards the strata are chiefly sandy, and present alternations of marine 
and terrestrial conditions, pointing to oscillations which especially 
affected the Rocky Mountain and western regions. The greatest develop- 
ment of the system is to be seen in the north of Utah and in Wyoming, 
where it presents a continuous series of deposits unbroken by any uncon- 
formability for a thickness of from 11,000 to 13,000 feet. The following 
table shows the character of these deposits in descending order : 
Laramie (Lignitic) group.—Buff and grey sandstones, with bands of dark clays 
and numerous coal-seams, containing abundant terrestrial vegetation of Ter- 
tiary types, marine and brackish-water molluscs (Ammonites lobatus, Inocera- 
mus problematicus, Ostrea congesta, Cyrena Carltoni, Physa, Valvata, &c.), and 
remains of fishes (Beryx, Lepidotus), turtles (Trionyx, Emys, Compsemys), and. 
reptiles (Crocodilus, Agathaumas, &c.). This group is by some geologists 
placed in the Tertiary series, or as a passage series between the Cretaceous 
and Eocene systems (see below). ‘Thickness in Green River basin 5000 feet. 
Fox Hills group.—Grey, rusty, and buff sandstones, with numerous beds of 
coal and interstratifications of strata containing marine shells (Belemnitella, 
Nautilus, Ammonites, Baculites, Mosasaurus, &c.). 'Thickness on the great 
plains 1500 feet, which in the Green River basin expands to 3000 to 4000 
feet. 
Colorado group.—Calcareous shales and clays with a central sandy series, and 
in the Wahsatch region, seams of coal as well as fluviatile and marine shells. 
Thickness east of the Rocky Mountains 800 to 1000 feet, but westwards in 
the region of the Uinta and Wahsatch Mountains. ; . 2000 feet. 
This group has been proposed and named by Dr. Hayden and Mr. Clarence | 
King to include the following sub-groups in the original classification of 
Messrs. Meek and Hayden in the Missouri region: 
Fort Pierre sub-group.—Carbonaceous shales, marls, and clays (Inoceramus 
Barabini, Baculites ovatus, Scaphites nodosus, Ammonites, Ostrea con- 
gesta, &C.). 
Niobrara sub-group.—Chalky marls and bituminous limestones (Baculites, 
Inoceramus deformis, I. problematicus, Ostrea congesta, fish remains). 
Fort Benton sub-group.—Shales, clays, and limestones (Scaphites warren- 
ensis, Ammonites, Prionocyclas Woolgari, Ostrea congesta). 
Dakotah Group, composed of a persistent basal conglomerate (which is 200 
feet thick and very coarse in the Wahsatch region) overlaid by yellow and 
grey massive sandstones, sometimes with clays and seams of coal or lignite 
(Dicotyledonous leaves in great numbers, Inoceramus, Cardium, &c.), 
Thickness 400 feet and upwards.! 
The extraordinary paleontological richness of these western Creta- 
ceous deposits has been already referred to. They contain the earliest 
dicotyledonous plants yet found on this continent, upwards of 100 
species having been named, of which one-half were allied to living 
American forms. Among them are species of oak, willow, poplar, beech, 
elm, dogwood, maple, hickory, fig, cinnamon, laurel, smilax, tulip-tree, 
sassafras, sequoia, American palm (Sabal), and cycads. The more cha- 
racteristic mollusca are species of Terebratula, Ostrea, Gryphea, Exogyra, 
Tnoceramus, Hippuvites, Radiolites, Ammonites, Scaphites, Hamites, Baculites, 
Belemnites, Ancyloceras, and Turrilites. Of the fishes of the Cretaceous 
sca many species are known, comprising large predaceous representa- 
tives of modern or osseous types like the salmon and saury, though 
cestracionts and ganoids still flourished. But the most remarkable 
feature in the organic contents of these beds is the extraordinary number 
1 Hayden’s Reports of Geographical and Geological Surveys of Western Territories ; 
King’s Geological Report of Exploration of 40th parallel, vol. i. 
