28 



with Tertiary forms ; that the species referred to Plastomenus constitute an 

 indication of affinity with corresponding Eocene forms. The presence of gar- 

 fishes of the genus Clastes in this formation is as yet peculiar to this and the 

 Judith River localities. As these gars have not heretofore been found in 

 North America below the Eocene, they constitute the first case of apparent 

 commingling of Tertiary and Cretaceous animal life yet clearly determined. 

 Yet the evidence is far from being as weighty in indication of Tertiary rela- 

 tions as is the presence of the saurians in question as evidence of Mesozoio 

 character; for the gars, though now living, are an ancient type, their allies 

 having swarmed in the Jurassic seas, and it is therefore altogether reason- 

 able that they should be found in fresh-water deposits of Cretaceous jmd 

 Tertiary age. The rarity of the former deposits accounts for the late date of 

 their discovery there. 



The longest known of these transitional faunae was discovered by Dr. 

 Hayden near the mouth of Judith River, in Montana. As determined by Dr. 

 Leidy, it embraces the following Vertebrata: Hadrosaurus mirabilis ; Palceos- 

 cincus costatus; Troodon formosus ; Aublysodon horridus; Bottosaurus? humilis, 

 Trionyx foveatus ; Clastes occiden talis {Lepidotus, Leidy) ; Lepidotus haydenii. 



The first four species of this list are Dinosauria, and hence diagnostic 

 of the Mesozoic age of the formation. The Clastes indicates relation to the 

 Milk River fauna. 



That the Judith River formation is Cretaceous would appear to have been 

 the suspicion of Messrs. Meek and Hayden when they originally described the 

 deposit and its invertebrate fossils. Leidy suspected that the species "indicate 

 the existence of a formation like that of the Wealden in Europe." 1 Meek and 

 Hayden 2 remark: "We are inclined to think with Professor Leidy that there 

 may be, at the base of the Cretaceous system, a fresh-water formation like the 

 Wealden. Inasmuch, however, as there are some outliers of fresh-water 

 Tertiary in these lowlands, we would suggest that it is barely possible these 

 remains may belong to that epoch.'' From the standpoint of the writer, 

 these beds would be at the top of the Cretaceous, and more or less related to 

 the Fort Union epoch. Mr. Meek expresses himself 3 cautiously with refer- 

 ence to ("ho age of the Fort Union and Judith River formations, as follows: 



■Pn of the Acadcnij of Natural Sciences. Philadelphia, 1800, p. ',:■. 



L.c. i -v.. ,,. 11 1. 

 [hiyilon's Anuua] Report foi 1872, p. 160. 



