30 TREE ANCESTORS 



forms glade thickets, and most of the bottom lands support thickets 

 of shrubby willows {Salix adenophylla, halsamifcra, chlorophylla, 

 etc.). The treeless moors are characterized by dwarf willows 

 {Salix myrtilloides) and dwarf birches {Be tula nana) and by Cassan- 

 dra calyculata, Kalmia glauca, Ledum palustre, etc. Although the 

 forests of this northern region are of little economic importance at 

 the present time in the thinly settled condition of most of this 

 vast region they are destined to be of incalculable value for fuel 

 and domestic construction and probably for pulpwood, mine props 

 and other purposes when the country shall have become opened 

 up and more thickly settled. 



THE ATLANTIC REGION 



The Atlantic region comprises that part of North America ex- 

 tending from about latitude 53° north southward to the Gulf of 

 Mexico and from the Atlantic seaboard westward to the prairie 

 country of the Mississippi valley, or to about the 95th meridian. 

 This region includes a very great variety of topography, climate, 

 and soils, covering as it does more than 40° of longitude and more 

 than 25° of latitude. Along its northern margin the transition to 

 the sub-Arctic region is fairly well marked, but the western bound- 

 ary is to be found somewhere in the transition zone from forest 

 to prairie — grass lands extending far to the east in Illinois and the 

 eastern forest extending long distances to the west along the valleys 

 of the principal streams of the prairie states. 



Physiographically tliis vast area includes the Laurentian Upland, 

 the Atlantic Plain, the Appalachian Highlands, the Interior Low 

 Plateau, and parts of the Central Lowlands and the Interior High- 

 lands (Ozark and Ouchita).^ The Atlantic region may, however, 

 be divided into three areas which are fairly well marked by the 

 character of the woodland. These are: (1) the Northern Ever- 

 green Coniferous forest; (2) the Deciduous or Hardwood forest, 



^ The terminology is that of the Committee of the Association of American 

 Geographers. Fenneman, N. M., Annals Assn. Am. Geog., vol. 6, pp. 19-98, 

 1917. 



