380 



p. S. MARTIN 



Fig. 1. Vegetation zones of eastern North America. Small, isolated 

 mountain-top populations of boreal forest in parts of the Appalachians 

 are not shown. The southeastern pine forests are considered part of the 

 deciduous forest formation in a broad sense. Taiga is mapped on the 

 basis of its savanna-like structure; floristically it is not very different 

 from boreal forest. P = prairie. 



Full-Glacial (Fig. 2) 



Of utmost importance to the student of animal and plant distri- 

 butions is the extent of Full-glacial biotic displacement. Following 

 Flint we may date this period as ending roughly 17,000 years ago. 

 In New Mexico the San Augustin Plains, 7,000 feet in elevation, 

 were occupied by forest with a spruce pollen frequency of 20% 

 (Clisby and Sears, 1956). In Postglacial time the spruce has dis- 

 appeared and non-arboreal species have become more important. 



In eastern North America there are only two radiocarbon-dated 

 pollen diagrams that may represent pollen sedimentation of the 

 Full-glacial period. From a piedmont marsh in unglaciated Pennsyl- 

 vania the peak in non-arboreal pollen lies 80 cm below a radiocarbon 

 date of 13,500 B. P. (Martin, 1958a). Apparently the formation of 



