270 
THE WASATCH FAUNA. 
in a fragmentary condition, and often distorted by pressure. The fractures 
of the surface are often of such a kind as to indicate that the bones have 
been in a plastic state (see the figures of StypolopJius Mans*), during which 
the fissures thus created in them have in many instances been filled with a 
siliceous limestone. This material now presents a rough external surface 
of great hardness, and sometimes incrusts the teeth in such a way as to 
render it a difficult matter to expose them. Nodules of the same material 
abound on the bluffs (see the Geological Eeport). Not unfrequently the 
bones are covered with an incrustation highly charged with the red oxide 
of iron, and this substance gives its characteristic color to a large percentage 
of the fossils, the others being generally black or dark brown. The light 
colors of our Miocene beds are almost unknown, and the bones are always 
much harder than these, or even than the fossils of the Bridger group of 
Wyoming. These facts, in connection with the reduced number of expos¬ 
ures of the beds, account for the comparatively small number of species 
obtained, and the feeble representation of certain groups, e. g., the Birds, 
Lizards, Rodents, etc.; nevertheless, a large number of individuals were 
obtained, and a considerable extent of country explored, and I believe that 
the synopsis above given is an approximation to the expression of the 
characteristics of the most abundant types, or the relative numerical rep¬ 
resentation in the fauna of the different genera, orders, etc. 
Comparison with the established scale of geological horizons of Europe 
has established the fact that the beds in question belong to the Eocene 
category, as I have already shownf to be true of the longer-known Bridger 
beds, of Wyoming. It remains to collate them with the numerous sub¬ 
divisions of that period. The differences between the Wasatch and Bridger 
faunae have been in part pointed out in my Report on the Vertebrate Fos¬ 
sils of New Mexico, 1874,f and may be more fully stated as follows: 
1. Divisions found in the Wasatch beds, not yet reported from the 
Bridger beds: Aves, genus Diatryma (Rallied to Gastornis)-, Mammalia, 
Tceniodonta, PJienacodus, Pantodonta, Meniscotlierkm, most species of Eyra- 
cotlierium. 
* Plate xxxviii. 
tProc. Amer. Philos. Soc., 1872 (February, July). 
f Annual Keport of Chief of Engineers, 1874, ii, p. 692. 
