240 GEOLOGY OF THE DENVEE BASES'. 



05O feet of marine Cretaceous strata overlain by 300 to 350 feel of fresh water beds. 



The succession of strata and thickness as estimated by Mr. W. H. Weed arc as follows, 



beginning at the base: 



1. Soli, dark clay sliales. 



-. Band of ferruginous sandstone with Avicula Imguiformis, Tnoceramus cripsii, 



Baroda wyomingensis, Placenticeras placenta, etc. 

 .".. Shales like No. 1. 

 1. Coarse gray laminated sandstone. 



5. < 'arbonaceous shales with bed of lignite at base 100 



G. Brown sandstone with great numbers of Cardium speciosum and a few other 



species ;;n 



7. Sandy shales 25 



8. Dark clay shales with concretions containing Baculites ovatits in lower portion 



and sandy bands and concretions near the top with a characteristic Fox Hills 

 fauna including — 



Xuenla sp. Liopistha (Cyinella) undata. 



Clisocolus eordatns. Pholodomya subventricosa. 



Callista nebrascensis. Mactra formosa. 



Tellina tequilateralis. Lunatia subcrassa. 



Tancredia americana. Baculites ovatus. 



The total thickness of this bed was not seen at any one place, but it is at least 

 350 feet. 



Immediately above these dark shales is a bed of greenish-yellow sandstone which 

 occasionally forms bluff exposures 50 or 00 feet high, but usually only slightly exposed 

 in sleep slopes and largely covered by wash from the softer and lighter-colored beds 

 above. This was taken as the dividing line between the marine and fresh water 

 beds, though no fossils excepting silicilied wood were found in the lower 200 feet of 

 the latter. The remainder of the section, about 300 feet in thickness, is apparently 

 conformable with the underlying beds, but is quite distinct from then) in color and 

 texture. It consists of alternations of light colored, soft, friable sandstones, clays, 

 and marls, with some seams of lignite and purplish carbonaceous bands, fossils 

 are abundant in the upper 200 feet, consisting of fragments of silicilied wood, bones, 

 and numerous invertebrates. The latter include the following species: 



Splueriuni reeticardiiiale. Goniobasis subhevis. 



Sphienuiu planum. (ioniobasis subtortuosa. 



Ohio dame. (Ioniobasis sp. closely related to 



Ohio cryptorhynchus. G. tenuicarinata. 



Anodonta propatoris. Campeloma vetula. 



Viviparus conradi. Vetrina ? obliqua. 



Helix vcternus. I'hysa copei. 



