356 HATCHER MARINE AND NON-MARINE FORMATIONS. [April 7, 



Non-Marine Equivalents of the Marine Beds of the Colo- 

 rado AND Montana Formations. 



Between the Dakota sandstones and the base of the Tertiary 

 there is in this region a number of formations the characters of 

 which are indicative of littoral, brackish, fresh water and terrestrial 

 conditions. 



The lowermost of these is the Eagle formation, consisting for the 

 most part of massive sandstones with intercalcated beds of lignite 

 and shales. This formation is known to have a considerable dis- 

 tribution in Montana and it doubtless extends northward into 

 Canada. In general it is not very fossilferous, but in places, usually 

 of very limited extent, it has been found to contain in considerable 

 abundance marine invertebrates, indicative of littoral ccnditions. 

 Although as yet no fresh water vertebrate or invertebrate remains 

 have been found in these beds, yet the nature of the materials com- 

 posing them and the manner in which the sandstones, shales and 

 lignites replace one another are indicative of an adjacent land mass, 

 and it is quite probable that they are to some extent at least of fresh 

 or brackish water origin. A few remains of terrestrial vertebrates 

 have been found in them. They afforded the type of Oniithomimus 

 grandis Marsh and other fragments of terrestrial dinosaurs. The 

 presence of these remains may be considered as additional evidence 

 of an adjacent land-mass. 



The Eagle formation is conformably underlaid and overlaid 

 respectively by the Benton and the Claggett formations. Its strati- 

 graphical position is nearly, perhaps identically, the same as that 

 occupied by the Niobrara farther to the southeast, and it was I think 

 quite properly correlated with that horizon by Mr. Earl Douglass, 

 though I should not be in favor of applying the same name, as was 

 done by Mr. Douglass, to formations so different in lithological and 

 faunal characters. From the nature of these deposits it is evident 

 that toward the close of the Benton there was in this region a 

 decided change of conditions which materially altered the charac- 

 ter of the sedimentation, and that the true marine conditions which 

 had prevailed continuously throughout the Benton gave place to at 

 least shallow waters and in part perhaps to brackish and terrestrial 

 conditions, though it is evident from the character of the beds 

 composing the Eagle formation that the transformation was by no 

 means so complete at this interval as during the preceding one 

 which witnessed the deposition of the Atlantosaurus beds and 



