462 CHARLES C. MOOK 
stained red by hematite, as the case may be. These grits, espe- 
cially the red ones, are frequently most abundant in the upper levels 
of the formation; it is in these upper levels that calcareous material 
is more scarce. Beds of sandstone, sometimes of considerable 
thickness, occur at various levels; these sandstones are made up 
principally of quartz, which is often well rounded; feldspar grains, 
either fresh or more or less altered, occur along with the quartz; 
in some beds grains of volcanic ash, both fresh and altered, are 
found; and in a few instances beds of coarse sand several feet thick 
are made up of volcanic ash. Limestone beds, usually not over a 
foot or two in thickness, are frequently found in a section; these 
are sometimes composed largely of the shells of small gastropods. 
They are more common near the base of the formation than in the 
upper members. The lower beds are often arkosic, considerable 
quantities of feldspar being present, often cemented to the accom- 
panying quartz and to each other by a calcite matrix. Thin beds 
of agate are found in some sections. 
Very coarse material is not found in the Morrison. Sandstones 
of a moderate degree of coarseness are common throughout the 
entire area of Morrison outcrops. Such sandstones are, however, 
on the whole thicker and more common in the western exposures 
than in the eastern. 
3. The Morrison contains internal structures of considerable 
interest. In the first place the various strata often appear to the 
eye to extend over considerable distances, but when detailed 
sections are made, even a few miles apart, and compared with each 
other, it is noticeable that the details of the sections vary con- 
siderably. A gradual thinning out of beds of one kind of material, 
and their replacement by another kind, is the rule in this formation. 
For all of this variation the general aspect of the formation in one 
locality is very much like that in another. This type of thing has 
been aptly described by Dr. Lee as “uniformly variable.’”’ In some 
cases the thinning out of beds is sudden, as in the case of the old 
stream channel exposed at the site of the old Marsh-Hatcher 
dinosaur quarry near Cafion City. 
The variation and at the same time the uniformity of the thick- 
ness of the formation are of special interest. The greatest recorded 
