SCIENTIFIC EXPEDITION TO NORTHEASTERN COLORADO 15I 



A large land tortoise, chiseled from the sandstone, was the most impor- 

 tant specimen secured. This was taken from a point about eight miles 

 west of the Buttes. 



The next work was done in the Laramie group on the east side of 

 Crow Creek about twenty miles northeast of Greeley. Here, naturally, 

 the fossils are of invertebrates. This place, like Fossil Ridge, is the 

 type locality for a number of species, but the fauna is characteristic of 

 fresh and brackish water lagoons. The shells are found in thick layers, 

 many of them in a very fine state of preservation. There is little altera- 

 tion of the material composing the shells, they weather freely from their 

 matrix, and the species show a resemblance to those of later faunas. 

 Hence these beds have a decidedly Tertiary aspect, but of their Laramie 

 age there is no room for doubt. 



On the return trip collections were also made at the mouth of the 

 Thompson and near the confluence of the St. Vrain and the South 

 Platte. At the former station a fossil leaf was found in the Fox Hills 

 sandstone of Cretaceous age. This has been determined by Professor 

 T. D. A. Cockerell as a species of Ficus, a genus of trees to which the 

 cultivated fig belongs. Near the mouth of the St. Vrain a large number 

 of fossil shells were obtained. Especially worthy of record is a fine 

 series of oysters,^ which weathered out from the soft matrix in perfect 

 condition of preservation. 



From the foregoing account it will be seen that of all the points 

 visited Pawnee Buttes alone furnishes vertebrate fossils. The other 

 localities are rich in invertebrate material, especially the bivalves, 

 gastropods, and cephalopods. At Fossil Ridge the fullest collections 

 were made. Another expedition should make collections and do strati- 

 graphic work there, in order that this one locality may be thoroughly 

 understood and the results published. 



The Fossil Ridge material has not yet been fully examined, but 

 there are at least the following species as the result of the expedition: 



Halymenites major Lx. Serpula sp. 



Chaetetes dimissus White Anatina sp. 



Memhranipora sp. Anomia raetiformis Meek 



' Oslrea clahra. 



