90 DEUXIÈME ASSEMBLÉE GÉNÉRALE 
tive characters from their birth or genesis, through their prime, intotheir 
decline and death. Through this unique opportunity for observation has 
been confirmed a view of evolution long shared by most if not all palæon- 
tologists, vertebrate and invertebrate, but naturally not understood or 
PRINCIPAL. FORMATIONS IN WHICH FOSSIL MAMMALS | 
ARE FOUND IN WESTERN UNITED STATES 
CHARAI ISTIC 
ACHARAOTENENC A AC ORRESS END GREAT PLAINS SECTION UE 
EUROPEAN MAMMALS FORMATIONS ci - AMERICAN MAMMALS 
E——— Bison | 
| 
lephas | 
AH | 
FOREST BEDS NORFOLK Equus 
: BEANCO— 
VAL D'ARNO SUPÉRIEURE E 
PIKERMI 
Pliauchenia 
Pliohippus 
ORIVE ST ALBAN 
[Trilophodon 







Equus stenonis 















= ILE A — — OREGQN CTION 


DEF ECRE MASCAL: Protohippus 
sANsAN MIOCENE MMM 4pnetops | 
SABLES DE L'ORLI Anchitherium | 


 EOCENE 
NEW MEXICO 
CERNAYSIEN 
CALC.GROS. DE MONS 

Fac-el 
Most recent geological subdivision of the American Tertiary. 
Showing that the successive sections in Montana, New Mexico, Wyoming, Utah, 
Oregon, and the Great Plains afford a complete history of the Tertiary, homotaxial with 
that afforded by the corresponding European formations. 
shared by other zoologists because of the essentially different nature of 
evidence. I refer especially to the theory of the definite or determinate 
origin ' and development of certain at least of the new adaptive struc- 
tures, apparently, but not certainly according to the principle to which 
WaaGex applied theterm mutation?. The mutation ofthe palæontologist, 
! Osporx, H. F. The Palæontological Evidence for the Transmission of Acquired 
Characters. Amer. Naturalist, Vol. xxiii, 1889, p. 562. 
? ScorT, W. B. On Variations and Mutations. Amer. Jour. Sci. Vol. xlviii, Nov. 
1894, pp. 355-374. 
