OLIGOCENE OF EUROPE, NORTH AFRICA, AND NORTH AMERICA 205 



The earlier theory as to the origin of these vast deposits was that tlicy 

 were due to great lakes w4iose borders were frequented by rich mammalian 

 life. As early as 1869 Leidy ' raised a doubt as to this lacustrine theory 

 in the following words: "While the geological formation makes it appear 

 that the fossils were deposited in ancient lakes, or in estuaries or streams 

 connected with the latter, it is strange that they exhibit no traces of fishes 

 or of aquatic molluscs intermingled with the multitude of relics of terres- 

 trial animals. The single mollusc known is terrestrial, and the turtles are 

 mostly land forms. Even mammals of decided aquatic habitat are absent. 

 With the exception of the shore-living rhinoceros and the beaver, no am- 

 phibious mammals have been discovered. While the fossil bones are in 

 perfect preservation, their original sharpness of outline without the slightest 

 trace of erosion indicates quiet water with a soft muddy bottom. . . . 

 The few turtles appear to be related to the swamp-living emydians. It 

 is remarkable that there are no crocodile remains.^ Where were these 

 creatures when the shores of the ancient waters of Nebraska and Dakota 

 teemed with such an abundant profusion of ruminating hogs and oreodons?" 



Despite this sagacious suggestion by Leidy that the mode of preserva- 

 tion of the animal remains did not support the lake theory, this theory 

 was generally maintained by all geologists and palaeontologists up to a 

 comparatively recent time. Finally a number of geologists, Gilbert^ 

 (1896), Haworth^ (1897), Davis ^ (1900), Johnson *> (1902) began to throw 

 more and more serious doubts on this theory. Thus Davis observed 

 (1900, p. 372): "Geologists have been too ready to explain the freshwater 

 Tertiary formations of the Rocky Mountain region as lacustrine in origin. 

 The large share of these deposits are prol^ably due to fluviatile or other 

 sub-aerial agencies." The same author drew comparisons with the pied- 

 mont, or flood plains of the Ganges, the Po, and the Hwangho. The coup 

 de grace to the lake theory was, however, given by the palaeontologists, 

 Matthew ^ (1899, 1901), Fraas ** (1901) and Hatcher " (1902), who set forth 

 convincing reasons for the theory of fluviatile or river channel and flood 



' Leidy, J., The Extinct Mammalian Fauna of Dakota and Nebraska, Philadelphia, 1869. 



* Crocodile remains have since been discovered; see p. 185, Loomis, 1904. 



' Gilbert, G. K., The Underground Waters of the Arkansas Valley in Eastern Colorado. 

 U.S. Gcol. Sun., 17th Ann. Rept., Pt. 2, 1896, p. 576. 



* Haworth, E., Physical Properties of the Tertiary (of Kansas). Univ. Geol. Surv. Kansas, 

 Vol. II, 1896, p. 281. 



^ Davis, W. M., The Freshwater Tertiary Formations of the Rocky Mountain Region. 

 Proc. Amer. Acad. Arts ScL, Vol. XXXV, no. 17, March, 1900, p. 372. 



^ Johnson, W. D., The High Plains and their Utilization. U.S. Geol. Surv., 22d Ann. 

 Rept., Pt. 4, 1902, p. 6.38. 



^ Matthew, Is the White River Tertiary an Eolian Formation? Amer. Natural., Vol. 

 XXXIII, 1899, pp. 403-408; and. Fossil Mammals of the Tertiary of Northeastern Colorado. 

 Amer. Mus. Nat. Hist., Mem. 1, Pt. 7, Nov., 1901. 



^ Fraas (ed. by Osborn) on the aqueous vs. eolian deposition of the White River Oligo- 

 cene of South Dakota. Science, n.s.. Vol. XIV, 1901, pp. 210-212. 



° Hatcher, J. B., Origin of the Oligocene and Miocene Deposits of the Great Plains. Proc. 

 Amer. Philos. Sac, Vol. XLI, 1902, pp. 113-131. 



