THE HABITAT OF THE SAUROPOD DINOSAURS 461 
The characters of the Morrison may be discussed under the 
following heads: (1) distribution, present and probable past; 
(2) lithology; (3) internal structures; (4) stratigraphic relations; 
(5) conclusions regarding conditions of deposition, physical processes 
dominant during the period of deposition, and middle Mesozoic 
history. 
1. The present distribution of the Morrison is indicated on a 
map compiled by the writer.‘ The formation outcrops along the 
eastern and western borders of the Rocky Mountains in Wyoming, 
Colorado, and New Mexico; in the rim of the Black Hills; in 
canyons in southeastern Colorado and northeastern New Mexico; 
around the borders of the Bighorn and Owl Creek mountains in 
Montana and Wyoming; in isolated uplifts in Wyoming; in 
canyons and mesa scarps in northwestern New Mexico, western 
Colorado, and eastern Utah; and in various other occurrences in 
the states mentioned. The outcrops are usually not extensive, the 
formation never being the country rock over a wide area. The 
total area in which Morrison outcrops occur is, however, very large. 
There are vast areas where the Morrison must unquestionably 
underlie younger formations. The areas in which the Morrison 
was formerly present, but from which it has been removed by 
erosion, are also very large, their exact size not being known at the 
present time.- The total area which was formerly covered by 
Morrison sediments must have been extremely large, very likely 
exceeding a million square miles in extent. As remains of sauropods 
are now found at practically every region of Morrison outcrops, it 
follows that the distribution of the Sauropoda in North America 
was also very wide. 
2. Lithologically the Morrison is composed of a variety of rock 
types. The formation is frequently described as a series of ‘‘ joint 
clays,’ fine-grained sediments which appear to be fairly well 
consolidated when dry, but which crumble or break readily when 
wet. These are red, brown, gray, or maroon in color. Petro- 
graphically they are fine grits composed mostly of quartz, with 
some argillaceous interstitial material which may or may not be 
t Charles C. Mook, ‘“‘A Study of the Morrison Formation,” Annals of the New 
York Academy of Sciences, XXVII (1916), 39-101, Pl. VI. 
