THE HUMAN OR PRESENT PERIOD 937 



the ice, occupies the barrens of the northern border of the con- 

 tinent; while the fur-clothed animals distributed themselves through 

 the three northerly zones, most notably the subarctic zone of the 

 conifers. 1 



The -westward spread of these floras and faunas of the south- 

 eastern regions seems to have been meager. In the west, the 

 southwestern arid and prairie floras and faunas seem to have had 

 the better of the contest with the forest forms, and to have spread 

 eastward in the mid-latitudes at the expense of the southeastern 

 group; at least arboreous vegetation is found appreciably farther 

 west in interglacial deposits than on the present surface. This 

 does not seem to be equally true in the higher latitudes, where the 

 trees of the eastern group are distributed far to the northwest. 



The arid and semi-arid floras and faunas of the southwest seem 

 to have pushed the more Boreal and arboreous forms to the north- 

 ward, or forced them to ascend the mountains; but the movement 

 was less sweeping and more complicated than that of the east, be- 

 cause of topographic interference and the effect of the lingering 

 mountain glaciation. 



In this re-dispersion of the North American faunas and floras 

 there is a world of suggestive detail of which only a small part has 

 been worked out into clear definition. From the viewpoint of in- 

 vestigation, it is a rich and almost virgin soil, forming the turn-row, 

 as it were, between the more cultivated fields of the geologic and 

 biologic sciences. Among other things, it seems not improbable 

 that studies on the rate of migration of plants to the northward, 

 after the last glaciation, may afford a basis for estimating the length 

 of post-glacial time. 



The Dynasty of Man 



Human dispersal. As yet there is little geological evidence 

 relative to the place of man's origin, or to the earliest stages of his 

 development. Various considerations connected with his physical 

 nature and his distribution seem to point to the warm zone of the 



1 Some of these and other features are suggestively discussed by C. C. 

 Adams, The Post-Glacial Dispersal of the North American Biota, Biol. Bull., 

 Vol. IX, 1905, pp. 53-71. 



