.J HATCHER — MARINE AND NON-MARINE FORMATIONS. 353 



beds as the Lakota formation and has discovered in them dinosau- 

 rian remains representing types differing from and distinctly more 

 recent than those commonly met with in the typical Atlantosaurus 

 beds. Moreover at several localities these transitional beds have 

 yielded cycads and other plant remains which, according to Prof. 

 L. F. Ward who has studied this flora, are of Lower Cretaceous 

 types. At present the dinosaurian fauna is too meagre to deter- 

 mine certainly whether its affinities are with the Jurassic or Lower 

 Cretaceous. Its aspect is however, in so far as we know it, more 

 modern than that of the typical Jurassic. The Predentata appear 

 to be assuming the predominant position held throughout the 

 Jurassic by the Sauropoda, and I am inclined to consider the dino- 

 saurian fauna as indicative also of a Lower Cretaceous age for these 

 beds. 



The Atlantosaurus beds, consisting of dark shales with inter- 

 calated sandstones, have a wide distribution throughout the western 

 portion of the region under consideration, where they appear at 

 the proper position in the geological section encircling every 

 mountain upthrust and occupying many of the intermediate val- 

 leys. These beds contain the remains of an exceedingly rich and 

 varied dinosaurian fauna, concerning the age of which there has 

 been some difference of opinion. At present, however, this fauna 

 together with the beds containing it is very generally regarded as 

 of Jurassic age. There are, however, certain geologists and paleon- 

 tologists who still regard these deposits as of Lower Cretaceous age. 

 The dinosaurs, which probably offer the most reliable evidences as 

 to the age of these beds, are unmistakably Jurassic in type, whether 

 the comparison be made between the individual species or the 

 faunas as a whole. Marsh was wont to correlate the Atlantosaurus 

 beds with the Wealden which he regarded as of Upper Jurassic age, 

 but which is now usually placed at the base of the Lower Creta- 

 ceous. It is not quite clear upon what evidence Marsh relied when 

 making this correlation. The dinosaurian fauna of the Wealden is 

 certainly quite different and more modern than that of the Atlanto- 

 saurus beds. In the Wealden the Sauropod dinosaurs, which form 

 such a conspicuous feature in the faunas of the Middle and Upper 

 Jura, are on the wane and that group of Predentate dinosaurs known 

 as the Iguanodontia has attained unusual importance, assuming to a 

 certain extent at least the position formerly held by the Sauroi)oda. 

 In the Atlantosaurus beds, however, the Sauropoda predominate and 



