THE DINOSAUR BEDS OF THE GRAND RIVER 
VALLEY OF COLORADO. 
During the spring of 1899, while in correspondence with Dr. S. M. 
Bradbury, President of the Western Colorado Academy of Science, 
the writer’s attention was called to the occurrence of vertebrate fossils 
in the Valley of the Grand River. The presence of these fossils had 
been locally known for fifteen years and they had been more or less 
collected as curios, but no paleontologist had investigated the matter 
and no report of their presence had been given to the scientific 
world. Knowing that the older collecting grounds for Dinosaur fos- 
sils were rapidly being culled, and aware of the possible importance 
of discovering a new field, plans were at once made looking toward 
the investigation of this locality. However, it was not until the fol- 
lowing spring that a Museum expedition could be organized and sent 
into this region for the purpose of collecting fossils. The three 
months so employed yielded such important returns that early in the 
past year the work was resumed with equally gratifying results. 
The Jurassic* formations of the Grand River Valley were orig- 
inally described by +Peale in the Survey of Colorado, but some 
further description, based upon observations made during the two 
summers spent there, and illustrated with photographs by Mr. H. 
W. Menke of the Museum, may be of interest. 
On the southern bank of the Grand River the Uncompahgre 
Plateau breaks away in a series of benches and folds to the level of 
the valley below. The western half of this plateau is made up chiefly 
of the Jurassic and Triassic formations, although retaining in many 
places a capping of lower Cretaceous. Farther west the Valley of the 
Dolores has cut through these formations into the underlying Car- 
boniferous. In the cafions formed by its tributaries, as well as those 
of the Grand River, the whole depth of the Jura-Trias is exposed. 


*These beds have been variously designated as: *‘ Lower Dakota Group” (Peale, U.S. Geo- 
logical and Geographical Survey of Colorado and Adjacent Territory, p. 179); ‘* Atlantosaurus 
Beds” (Marsh, Amer. Jour. Sc., third series, Vol. XXI., p. 411), and “Como Beds” (Scott, An 
Introduction to Geology, p. 477; Williston Amer. Jour. Sc., fourth series, Vol. XI.. p. 114). While 
the consensus of opinion among later writers would place the fresh-water deposits in the lower- 
most Cretaceous, contemporary with the English Wealden, for reasons which will later appear they 
will be referred to in this article as Jurassic. 
tPeale, op. cit., p. 170-180. 
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