1 86 The Tertiary Formations of the [March, 



Amyzon beds. In its petrographic characters it is most like the 



The writer first referred the Wasatch to the Eocene division of 

 the Tertiary, it having been previously regarded as Miocene. 

 (Proceedings American Philosophical Society, February, 1872.) 



The vertebrate fauna of the Wasatch is rich, and presents many 

 peculiarities. Prominent among these is the presence of the 

 strange Coryphodontidce, which reached a great development at 

 this time. Also the Phenacodontidce, and the genus Hyraco- 

 therium. These are the ancestral types of the hoofed mammals, 

 and they were associated with numerous flesh-eaters of partly 

 marsupial character. It is nearly identical with that of the 

 Suessonian of Western Europe, which is at the base of the Eo- 

 cene series. The fullest account of it is that which I have given 

 in the Report of Captain Wheeler of Explorations and Sur- 

 veys west of the 100th meridian, Vol. iv. 



" This is one of the more important of the groups among those 

 that, in Western North America, are referred to the Tertiary 

 period, especially as regards the vertebrate remains that have 

 been obtained from its strata. It is most fully and characteristi- 

 cally developed in the region known as the Green River basin, 

 north of the Uinta mountains, only the south-eastern portion of 

 the formation, so far as is now known, extending into North- 

 western Colorado. In its typical localities it is found resting con- 

 formably upon the Green River group, into which it passes with- 

 out a distinct plane of demarkation among the strata. 



" Its molluscan fossil remains correspond closely with those of 

 the Green River group, some of the species being common to 

 both, all indicating a purely fresh condition of the waters in which 

 the strata of both groups were deposited. At the typical locali- 

 ties the group is composed in great part of soft, variegated, bad- 

 land sandstones, a peculiar greenish color often predominating 

 over the others, which are reddish, purple, bluish and gray. 

 Limestone strata, marly and clayey beds, and cherty layers are 

 not uncommon, and grits and gravelly layers sometimes occur." 



To the above general remarks of Dr. C. A. White I add, that 

 the material of this formation consists of indurated clays more or 

 less arenaceous, which display various degrees of hardness. The 

 harder beds are, however, thin, and the intervening strata yield 

 readily to meteoric influences. They are frequently quite arena- 



1 See American Naturalist, April, 1880. 



