358 B. BROWN CRETACEOUS-EOCENE CORRELATION IN NEW MEXICO 



Through this eastern exposure I have often found it impossible to estab- 

 lish any definite line of demarcation between the two beds. 



The insensible gradation from marine through brackish-water into 

 fresh-water sandstones is not confined to the eastern exposures of the 

 "Lance" on Hell Creek. The same transition is found on the border of 

 the Lance fonnation on Alkali Creek, Seven AEile (Jreek, and Robber's 

 Eoost, all tributaries of the Cheyenne River in Weston County, Wyoming. 



No sign of an angular unconformity has been noted between the Fox 

 Hills and the "Lance," and I have never yet seen any geologic evidence 

 of the "great diastrophic break" which is alleged to occur here. 



The actual geologic history appears to be as follows : There were areas 

 in close proximity during the close of Fox Hills times where denudation 

 was taking place simultaneously with deposition. In the case of the 

 nonconformity, there was a cutting off and drying up of an area without 

 freshening before the beginning of littoral deposition; in the other case 

 there occurred the isolation of an arm of the sea and a gradual freshen- 

 ing of the impounded waters before drying up. 



The lithologic structure of the Hell Creek beds is similar in nearly 

 every respect to that of the Lance of Converse and Weston counties, 

 Wyoming. Most genera and species of vertebrates and invertebrates are 

 common to both deposits, and the faunal facies may be considered a unit. 



List of Fauna and Flora 



VERTEBRATES 



Mammals : 



Ptilodus sp. 



Meniscoessus conquistus Cope 



Meniscocssus sp. 



Reptiles : 

 Triceratops serratus Marsh 

 Triceratops brevicornus Marsh 

 Triceratops sp. 

 Trachodon mirahilis 

 Trachodon annectens Marsh 

 Trachodon sp. 



Thcscelosaiirus ncglectus Gilmore 

 Ankylosaurus magniventris Brown 

 Palaoscincus sp. 

 Tyrannosaurus rex Osborn 

 Auhlf/sodon sp. 

 Ornithomimus alius f Lambe 

 Champsosaurus laramiensis Brown 



Champsosaurus ambulator Brown 

 B rachychampsa montana Gilmore 

 Lcidyosuchus sternhergii Gilmore 

 Basilemys sinuosa Riggs 

 f Adocus lineolatus Cope 

 Compscmys victa Leidy 

 Compscmys ohscura Leidy 

 Helopnnoplia distinctq 

 Aspidcretes sp. nov. 

 Aspidcrctes (Trionyx) foveatus Leidy 

 Aspidcretes heecheri Hay 

 Scapherpeton tectum f Cope 

 Diphyodus sp. 

 Rhinenstcs sp. indet. 

 Piippichthys sp. indet. 

 ><<<rphirhyHchus 

 Lcpisftstcus occidcntalis 

 Lamna. sp. 



