72 GEOLOGY OF THE DENVER BASIN. 



iron oxide is distributed throughout its entire mass. It is fine-grained, of 

 close texture, and usually occurs as a single bed. Occasionally it becomes 

 concretionary. It is in close union with the basal sandstone of the Laramie; 

 no transition bed exists; the passage from the one to the other is direct; 

 combined they frequently enter into the formation of a single bluff 150 

 feet high. Notwithstanding this, the formations are easily distinguished by 

 their lithological contrasts and by the fossil horizon marking the summit of 

 the older. 



LIFE. 



"While invertebrate fossil remains occur throughout the entire thickness 

 of the Fox Hills, there is an especially conspicuous array of characteristic 

 forms at the very summit of the formation, in the uppermost layer of the 

 capping sandstone, none of which is ever found above, and lint few of 

 which are met with in numbers below. This is, moreover, a paleontological 

 feature of the formation in all its western localities. Among the forms 

 found in the Denver field those especially characteristic are — 



Mytilus subarcuatus, Crenella elegautula, 



Nucula cancellata, Cardium (Ethmocardium) speciosum, 



Solemya snbplicata, Sphaeriola cordata, 



Veniella humilis, Callista deweyi, 



Oallista (Dosinopsis) owenana, Mactra alta, 



Tell'ua scitula, Tancredia americana, 



Liopistha (Cymella) uudata, Fasciolaria cheyennensis, 



Pyrula bairdi, Fnsus sp. .' 



Pseudobuccinum nebrascense, Anchura americana. 



Turitclla sp. ? Dentalium sp. .' 



Oylichna sp. .' 



In plant life Halymenites major is generally met with in the upper 

 portion of the formation, in both the sandstones and the limestones. 



LARAMIE FORMATION. 



The entire Denver field, excepting the belt along the foothills occupied 

 by the older formations, is underlain by Laramie strata, but their surface 

 exposures are confined to the northern and northeastern portions of the 

 field and to a narrow strip parallel with the foothills at a distance from 

 them of between 1 and "_' miles. 



