SEPT. 1901. Dinosaur BEps oF Gr. River Vau’y, Co,t.—Riccs. 271 
In this section the massive sandstone ledge is the characteristic 
Dakota sandstone referred to in the eastern Gunnison region as 
marking the base of the Cretaceous. From its well-known lithologi- 
cal character, as well as the abundance of dicotyledonous leaves found 
in it, there can be no doubt that it is the same which caps the Como 
Beds* at Cation City and Trinidad, Colorado, and at Como Bluff and 
in the Freezeout Hills of Wyoming. In fact so persistent is this 
ledge and so marked is its effect upon the land sculpture, owing to its 
resistance to erosion, that it has come to be expected as a capping 
ledge wherever the beds occur. The variegated marls have the same 
lithological characters as the upper measures of Como Bluff and have 
been lately reported} from Trinidad, Colorado. 
The dark colored sandstones described under 3, though per- 
sistent at approximately the same level are by no means continuous. 
The writer has traced this level from the valley of the Gunnison to 
the point where Grand River enters the cafion and in a distance of 
twelve miles these ledges thin out and re-appear no less than five 
times. At the mouth of the No-thoroughfare Cafion, the sandstone 
strata are wanting entirely and the clays show not only a continuous 
deposition from the marine Jura to the base of the Dakota sandstone, 
but the color-banding grades evenly from the green shale below to the 
banded clays above. The same is quite as true at other points where 
the sandstone ledges thin out. 
Moreover, the characteristic fossils of the Como Beds occur more 
abundantly in the variegated clays than in the green shales below. 
Nowhere are they so abundant as in the cross-bedded sandstone 
ledges. Representatives of a single genus (Morosaurus) have been 
observed to range through the entire series. It is therefore evident 
that no important sub-division can be made of these beds. Whether 
Jurassic, as they have been usually considered, or lowermost Cre- 
taceous ‘and contemporary with the Wealden, as held by some, these 
measures should be regarded as identical with the Como Beds and 
treated as a close series having only such sub-divisions as are sug- 
gested on page 269. And if stratigraphy is of any value in determining 
the relationships of formations, the closely connected series of sedi- 
ments extending from the base of the marine Jura to the base of the 
_ Dakota sandstone certainly has a story to tell. Here, as in many 
localities observed throughout the states of Colorado and Wyoming, 
the marine Jura and the fresh-water beds are so intimately related as 
to admit of no hiatus. If it then be proved that the relations of the 
*Scott, An introduction to Geology, p. 477, Williston Amer. Jour. Science, Vol. XI., p. 114. 
tLee, Journal of Geology No. 4, 1901. 
