L INTRODUCTORY REMARKS. 



beds of the Upper Missouri Lignites near Moreau and Grand Rivers, Nebraska, 

 very probably belonging to the horizon of the Judith River group, some ver- 

 tebrate remains, which have been considered Cretaceous types by Professor 

 Cope. The latter irentleman has also described from branches of Milk River, 

 in British America, some Dinosaurian and other vertebrate remains, collected by 

 Dr. Dawson, geologist of the British North American Boundary Survey, which 

 he regards as proving the beds from which they came to be of Cretaceous 

 age.* In his large report on the Cretaceous Vertebrata of the West, issued 

 in 1875, Professor Cope again refers the Judith River vertebrates, and all of 

 the others from the several other localities in the Upper Missouri country 

 mentioned, to the Cretaceous, but assigns the whole to the Fort Union group. 

 To the writer of these remarks, however, there seems to be very little reason 

 to doubt that the beds from which nearly if not quite all of these Cretaceous 

 types of vertebrates came, belong to the horizon of the older brackish- and 

 fresh-water beds at the mouth of Judith River, for which the name Judith 

 River group has been used. 



That these older beds (the Judith River brackish- and fresh-water depos- 

 its and their equivalents elsewhere) are Cretaceous, is certainly highly prob- 

 able, as has been suggested by the author on, former occasions ; yet this can 

 scarcely be properly regarded as an established fact. The presence of the 

 Dinosaurian and other types of vertebrate remains in them, unlike any of the 

 forms found in other parts of the world in later than Cretaceous rocks, is 

 undoubtedly a very strong argument in favor of the conclusion that they 

 belong to that epoch. On the contrary, however, some Eocene types of ver- 

 tebrates have also been found in these beds at certain localities, such, for 

 instance, as Plastomenus, a Tortoise, the type of which is from the Eocene 

 of Wyoming and New Mexico ; and remains' of Garfishes of the genus Wastes, 

 discovered by Professor Dawson on branches of Milk River, in beds almost 

 certainly of the same age as those of the typical Judith River locality, where 

 the last-mentioned genus also occurs along with the Cretaceous types of Sau- 

 rians. Some of the plants described by Professor Lesquereux, and regarded 

 by him as decidedly Eocene, seem also to come from beds belonging to this 

 horizon. 



Respecting the occurrence of the Judith River group at other localities 



* See Dr. Dawson's Report on the Geology of the British North American Boundary Survey, p. 

 333 ; Montreal, 1875. 



