94 DEUXIÈME ASSEMBLÉE GÉNÉRALE 
rica. Many able contemporary workers, especially ScacLosser and DEPÉ- 
rer, are also bringing forth new illustrations of this law in Europe. 
II. PROGRESS OF DISCOVERY AND THE NEW PHYLOGENETIC PROBLEMS 
SUGGESTED THEREBY 
My purpose in this section is to give a brief resumé of the progress 
during the past ten years, and in our present state of knowledge to point 
out where exploration and research should principally be directed. 
The general advance has been made in five distinct lines, which 
appear to mark out also the main lines for future research. First, the 
biological value of more accurate geological records (Compare Fig. 1), 
has been recognized; as a result the mammalia have been chronologically 
segregated into successive life zones similar to those which have long 
been developed in invertebrate palæontology; these life zones in some 
cases subdivide not only the periods (Eocene, Miocene, etc.), but also sub- 
divide the stages (Bridger, Uinta), ete. Second, notonly have these clearer 
chronological subdivisions been made, but the faunas have been se- 
parated according to their kinds and the nature of the deposits, into 
those which inhabited respectively the lowlands and rivers, forests, 
plains, and uplands. The advance of physiography has been felt, and by 
the carefui work of Harcner‘, Marraew ?, and Grpzey*, the theory of 
fluviatile, Hood plain, and æolian deposits has tended to replace the 
theory of great lakes or lacustrine deposits. Third, there has accor- 
dingly been brought about a modification of our views as to the meteo- 
rological or climatic phases of the tertiary period, in the direction of 
extending the idea of the existence of great dry plains with drifting sands 
favorable to Æolian deposits chiefly in the Lower Pleistocene, Pliocene 
and Miocene; we speak less of a moist, subtropical, and more of a drier 
climate. Fourth, the zoogeographical relations of the North American 
faunas to those of other continents have become much more clearly un- 
derstood (OsBorx°) in connection with more exact geological records not 
1 Origin of the Oligocene and Miocene Deposits of the Great Plains. Proc. 
Amer. Philos. Soc., xli, No. 169, Apr. 1902. 
? Isthe White River Tertiary an Æolian Formation. Amer. Nat., xxxiii, May, 
1899, pp. 403-408. 
# Fossil Mammals of the Tertiary of Northeastern Colorado. Mem. Amer. Mus. 
Nat. Hist., Vol. 1, Pt. vii, Nov. 1901. 
# The Freshwater Tertiary of Northwestern Texas. Bull. Amer. Mus. Nat. Hist. 
Vol. xix, 1903, pp. 617-635. 
® Marraew and Giozey. New or Little Known Mammals from the Miocene of 
South Dakota. Bull. Amer. Mus. Nat. Hist., Vol. xx, pp. 241-268. 
5 Faunal Relations of Europe and America. Science, Vol. xi, April, 1900, pp. 
561-514. 
roms 
