272 FiELD CoLuMBIAN MusEuM—GEOLOGY, VOL. I. 
fresh-water fauna to that of the Wealden indicate contemporaneity 
rather than an accelerated development of reptilian life in America, as 
might well be the case, we must conclude that the barren zone of 
green clays lying between the marine Jura-and the fossil-bearing hori- 
zon has bridged the gap between Jurassic and Cretaceous. 
From their lithological characteristics, as well as the nature of 
their weathering, the variegated clays might well be mistaken for 
Eocene bad lands. ‘They are made up of the same sort of indurated 
clays, firm as sandstone under the pick, but readily dissolved and 
yielding rapidly to erosive agencies. There is also the same brilliant 
horizontal banding, the same nodular layers, the same cross-bedded 
and interrupted ledges of sandstone, and the same variation of hard 
and soft strata which gives the characteristic bench-like profile com- 
mon to these formations. In short, so close is the resemblance to the 
Wind River Eocene of central Wyoming that were it not for the fos- 
sils one might be justified in regarding the two as identical. 
™ OCCURRENCE OF FOSSILS. 
The fossils found in this region are, with few exceptions, verte- 
brate. One invertebrate fossil (Vivifarus) is found abundantly in 
one or two localities and is of interest in being chalcedony-filled. 
The vertebrates so far as observed, are confined to the order Dino- 
sauria, but are quite abundant. The forms are the common types of 
the Como Beds as found in eastern Colorado and in the well-known 
localities of central and southern Wyoming. 
As before stated, the marine beds have so far produced no fos- 
sils, and the greater part of the green shale of the lower fresh-water 
beds seems to be barren. The lowest point at which fossils have been ° 
found is twenty feet below the top of these beds. From this point 
upward they rapidly increase in abundance. In fact the thin stratum 
of dark shale, lying just below the cross-bedded sandstone, and the 
lower ledges of this sandstone are the richest in fossils of all these 
deposits. In certain localities however, the whole series of sandstone 
abounds in fossils. In the variegated clays, Dinosaurs have been 
found at all levels from the base to within a few feet of the capping 
Dakota sandstone, but are usually confined to the lower 150 feet. 
No general deposits of fossils such as are found in eastern Colo- 
rado and southern Wyoming have been discovered in this locality. 
In the clays seldom more than one individual is found in a place and 
these have the bones but little displaced from their relative positions. 
