382 p. S. MARTIN 



in the unglaciated Appalachian Plateaus "... appear to be most 

 common in pastures, but field and woodland areas are not entirely 

 free from such movements" (Sharpe and Dosch, 1942). 



Wolfe's description (1953) of frost-thaw basins and related peri- 

 glacial features in unglaciated New Jersey has been subjected to 

 certain criticism. Yehle (1954) questioned the authenticity of the 

 alleged frost cracks. Rasmussen (1953) and Deevey (1957) noted 

 that basins of rather similar appearance occur in the Carolinas and 

 coastal Texas, beyond the limit of possible periglacial frost action. 

 However, the involutions and ventifacts which Wolfe described 

 would appear to remain sound evidence of a periglacial tundra 

 climate. 



Farther south, in the latitude of Washington, D.C., Hack (1955) 

 and Nikiforoff (1955) found little geomorphological indication of a 

 "periglacial climate," beyond stabilized dunes and a soil hard pan of 

 uncertain origin. For this reason, I have included this area within 

 the Boreal Forest (Fig. 3). 



In the Appalachians the block fields or stone streams (Flint, 1957) 

 and glades including "bear wallows" may mark the lower limit of 

 Full-glacial alpine tundra (Braun, 1955; Martin, 1958a). Cranberry 

 Glades in West Virginia at 3,350 feet (Darlington, 1943) is perhaps 

 the best known of the anomalous glade bogs; Core (1949) discussed 

 others. In the Smoky Mountains inactive block fields covered with 

 mosses and ferns and occasional yellow birch trees extend down to 

 at least 4,500 feet. Braun (1955, p. 361) believed that they indicate a 

 vertical tree line depression of 2,000 feet. It seems the present 

 regional tree line does not lie at the top of the peaks as Braun im- 

 plies. Spruce and fir grow as forest at 6,500 feet, the top of the 

 Smokies (Whittaker, 1956). I would allow an additional 2,000 feet 

 for subalpine taiga and "krumholtz" and locate the theoretical 

 present alpine zone at 8,500 feet. This would bring the relative 

 depression of the Alpine Zone in eastern North America into line 

 with that observed at the same latitude in the west, 4,000 to 4,500 

 feet (Antevs, 1954). In either case the distribution of glade bogs and 

 inactive block fields reveals that a Full-glacial treeless zone extended 

 down into the Great Smokies. 



To the south of the region of a periglacial treeless zone we might 

 expect buried organic soils, fossilized "string bogs," or organic ter- 

 rain of the type that typifies subarctic taiga and boreal forest (Drury, 



