R. S. Lull — Dinosaurian Distribution. 9 



colubrid snake. "which makes fair progress in the water, not- 

 withstanding the absence both of a compressed tail and of a 

 vertical fin." 



The Wealden formation of England is thus described by 

 Geikie (1903, pp. 1180-1181). "The Purbeck beds bring 

 before us evidence of a great change in the geography of 

 England towards the close of the Jurassic period. They show 

 how the floor of the sea, in which the thick and varied forma- 

 tions of that period were deposited, came to be gradually 

 elevated, and how into pools of fresh and brackish water the 

 land leaves, insects, and small marsupials of the adjacent land 

 were washed down. These evidences of terrestrial conditions 

 are followed in the same region by a vast delta formation, that 

 of the Weald, which accumulated over the south of England, 

 while the marine strata were being deposited in the north. 

 Hence two types of Lower Cretaceous sedimentation occur, 

 one where the strata are fluviatile (Wealden), and the other 

 where they are marine (Neocomian)." 



In Wyoming the Morrison beds lie directly upon the marine 

 Baptanodon beds of Marsh in which Belemnites abound. 

 Lying between this and the main dinosaur-bearing layer are 

 about 156 feet (Loomis 1901, pp. 192-193) of variegated sand- 

 stones and clays, of which bed No. 13, 82J feet above that 

 which contains Baptanodon itself, seems to represent the first 

 of the freshwater (or brackish) series, as it contains an aban- 

 doned dinosaur quarry in Como Bluff. This would seem to 

 indicate that in the Morrison, conditions very similar to that 

 of the Wealden prevailed and that in each instance access to 

 the sea on the part of the sauropod inhabitants was not only 

 possible but actually probable, as the littoral realm seems to 

 have been the highway of immigration of this order of dino- 

 saurs. 



The Morrison beds, lying as they do in a great synclinal 

 trough, and at the time of their deposition but little above sea 

 level, probably were drained, in the southern portion at least, 

 into the sea, which lay some two hundred and fifty miles 

 (Schuchert 1909, Late Upper Jurassic Chart) to the south- 

 ward. This drainage outlet because of its very low gradient 

 may again have given conditions similar to those of the 

 Amazon (vide supra p. 8), so that the passage of the 

 Sauropoda across the area included in the present state of 

 New Mexico would appear to have been perfectly feasible. 

 Evidence which may be corroborative is found in Madagascar, 

 in a locality east of the bay of Narinda, wherein were dis- 

 covered the remains of Titanosaurus in a matrix containing 

 the marine Mytilus madagascarensis and foraminifera (Boule 

 1896, p. 348). 



