670 THE GEOLOGICAL AGE OF THE COAL OF WYOMING. 
age of the coal series of the west, and the exact line of demare- 
ation between the Cretaceous and Tertiary periods.” (Report 
1870 pp. 164-5.) Thus Prof. Hayden left the subject at that time. 
In passing over the region from Ft. Bridger to Black Buttes 
during the present season, I traversed successively the strata of 
the Bridger and Green River epochs. Near Rock Spring Station 
the coal group makes its appearance, rising from beneath the 
Green River strata, as it appeared to me without instrumental 
aid with some degree of uncomformability. This forms the west- 
ern border of an upthrust of rocks of which Dr. Hayden has treated 
in the above extract. At Rock Spring eleven coal beds have been 
struck in shafting, of which the upper and thickest is ten feet 
in depth. The rocks are buff sandstone néarly worn, alternating 
with gray sandstones and shales. They descend again near Point 
of Rocks and remain nearly level at Black Buttes. At Hallville 
I obtained isolated scales of numerous species of fishes. At 
Black Buttes I learned that Mr. F. B. Meek had visited the 
neighborhood, and had discovered the bones of some large animal. 
I went to the spot and found fragments of large bones lying m 
a bed of fossil leaves. On excavating, other bones were obtained 
including sixteen vertebrae, the sacrum, both ilia and other pelvi 
bones, with ribs and bones of the limbs. The position of the 
bones was in a bed of gray sandstone, above one coal bed and 
below two. They were covered with the leaves. which had evi- 
dently falien upon them, and filled the intervals between them, 
and occupied the angles between the processes, the neural canal, 
etc., just as they had been pressed in when soft. The skeleton had 
fallen on the shore, for the leaf bed passed gradually into a 
bed, which included mostly thin bivalved species. 
The pelvic and sacral bones, in fact every part of the skeleton 
proved the reptile to have been a Dinosaurian. The a 
dorsal vertebra was twenty-eight inches in height and the ilium 
between three and four feet in length; both extremities arè 
straight, the one massive, the other dilated and thin, with a supè 
rior process. It resembles that of Cetiosaurus more than any — 
other but presents well defined differences. It is named Aga 
thaumas sylvestris. 
This discovery places this group without doubt within the limi 
of the Cretaceous period, and to that age we must now refer the 
great coal area of Wyoming. It is surrounded to 
a ee oO En Nat 
