Sept. 1901. Dinosaur Beps or Gr. River Vat’y, Cot.—Riccs. 269 
the igneous rock. The whole thickness of these ledges is about 400 
feet. 
The Jurassic strata range from 600 to 700 feet in thickness and 
may admit of four sub-divisions (Plate XXXIX). The lower or 
marine Jura is from 100 to 120 feet in thickness and consists of bluish 
and grayish gypsum-bearing clays in which thin layers of fine-grained 
sandstone and nodular ledges of limestone are interspersed. The 
latter are never more than six or eight inches in thickness and are 
usually from three to five in number. In no instance were fossils 
found in these measures. The change from marine to fresh-water Jura 
is scarcely noticeable and can be traced only by the absence of lime- 
stone and the more homogeneous and massive nature of the clays. 
There is, however, near the base of the fresh-water formation a ledge 
of fine-grained brown sandstone which is noticeable from its peculiar 
honeycomb weathering. 
Above the marine Jura hes a stratum of greenish clay shale about 
100 feet in thickness. It contains occasional ledges of homogeneous 
green sandstone and a few layers of clay nodules, but nowhere is there 
a marked color-banding. Above the green shale, which may be 
spoken of as the lower beds, comes a darker zone of 40 or 50 feet 
containing frequent ledges of cross-bedded sandstone. These vary 
from a fine-grained sand occurring in thin layers to a massive 
coarse-grained sandstone, rich in iron and weathering to a brownish 
red color. The latter sometimes reaches a thickness of 20 feet 
toward the western end of the exposures described. Throughout 
the series there is a noticeable tendency toward thinning out and 
being replaced at slightly different levels. In places the sandstone 
disappears entirely and the green shales below grade into the banded 
clays above. 
The variegated clays reach a thickness of 300 or more feet and 
are conspicuous on account of their brilliant horizontal banding as 
well as the typical bad-land shapes into which they weather (Plate 
XXXVIII). The alternation between green and purplish bands does 
not mark any variation in the nature of hardness of these massive 
joint clays. There are frequent layers of clay nodules, sometimes 
calcareous, and a few ledges of nodular gray sandstone which are 
confined to limited areas. Occasional thick ledges of cross-bedded 
sandstone and lenticular masses of greenish sand occur at almost all 
levels, but these are lhkewise of limited extent. Throughout the 
lower measures of this horizon. are abundant nodules of secondary 
formation, sometimes occurring in irregular strata, but often scattered 
promiscuously through the clays. Near the top the banding is least 
