470 The American Naturalist. [May, 
in virtue of isostatic equilibrium in a crust heterogeneous as to density.— 
G. K. GILBERT, in Bulletin. Geol. Soc. America. 
Scott and Osborn on the Fauna of the Brown’s Park 
Eocene.!—This memoir supplies an important desideratum, since we 
obtain through it the first intelligible view of the Mammalian fauna 
of the Brown’s Park or Uinta (name preoccupied) horizon of the 
Eocene of North America. This formation, as is well known, occupies 
the summit of the Eocene series, and therefore intervenes between the 
Bridger below and the White-River above. The faunz of the last- 
named horizons are tolerably well known, while for the Brown’s Park 
series we have had to depend hitherto on the exceedingly unsatisfactory 
descriptions published by Marsh many years ago. The formation has, 
so far as known, a limited geographical extent, occurring at the south 
base of the Uinta Mountains in N. E. Utah only. This location was 
explored by the Princeton party under Professor W. B. Scott, whose 
observations on the geology constitute the introduction to this memoir. 
The paleontological part of the memoir is an excellent model of 
what such a work ought to be, and the results are worthy of the care 
bestowed on its preparation. The species observed are eleven in number, 
which belong to as many genera. These areas follows: Quadrumana, 
yopsodus ; Gres, Plesiarctomys ; Creodonta, Mesonyx and Miacis ; 
Perissodactyla, Epihippus, Diplacodon, Isectolophus, Amynodon and 
Triplopus ; Artiodactyla, Protoreodon and Leptotragulus. Of these 
genera, Isectolophus, Protoreodon, and Leptotragulus*were discovered 
by the Princeton expedition. Nothing of unusual novelty is stated 
with regard to the species and genera of the Quadrumana, Glires, and 
Creodonta, but the case is quite different with regard to the Ungulata, 
Ancestral forms of later types are here most distinctly indicated, and 
the authors must be congratulated on the important contribution they 
have thus made to the doctrine of evolution. They show that Epihip- 
pus stands in the line of the horses, as asserted by Marsh, but, unlike 
that author, they satisfactorily demonstrate that it intervenes between 
Pliolophus and Anchitherium. They also show that Diplacodon is 
the ancestor of the varied forms of the Menodontidz of the lower 
Miocene, and the descendant of Palacosyops of the Bridger Eocene. 
Isectolophus is proven to be the parent of the tapirs, connecting that 
} The Mammalia of the Uinta Formation. 
lations, and Part II., the Creodonta, Rodenti i a s 
IL, The Perissodactyla, and Part IV., The Evolution of the Ungulate Foot, by H. F. 
Transactions of the American Philosophical Society, Philadelphia, 1889, Vol. 
XVI., p. 461; pl. V.; p. 112. aiy 
