FREE INSTITUTE OF SCIENCE 



35 



THE LIFE FEATURES OF THE COASTAL PLAIN AND THE PIEDMONT ^ 



gives outlooks over this lower country which to most of us are well-known sites 

 — Fox Chase, George's Hill in Fairmount Park, the ridge above Wayne Junc- 

 tion and the Midvale Steel Works, the Baltimore Pike at Primos, Swarthmore 

 College, and Allen's Hill near WalHngford, are some of the more famihar points 

 of overlook. Back of this "upland terrace" the hill and dale scenery of the 

 Piedmont Plateau stretches away to the north and west. 



II 



This boundary not only separates two strongly contrasted physiographic 

 areas, but Hkewise forms a dividing line between a more northern and a more 

 southern life, a frontier in the distribution of certain species of animals and 

 plants. As is well known, the continent of North America is primarily di- 

 vided into two great life regions, — a northern or "boreal" and a southern or 

 "austral," — each one of which is characterized by certain types of plants and 

 animals, the southern and northern ranges of which are restricted along a more 

 or less narrow intervening territory, the so-called "transition zone," where 

 many of these northerly and southerly species mingle. It is thus a region of 

 overlap, and fully justifies its name. These two contrasted primary areas 

 probably represent, as Merriam* has pointed out, a geographic division of 

 life as the result of temperature conditions, especially in relation to the period 

 of reproductive activity. The division has, however, a much wider signifi- 

 cance than the present conditions of temperature would imply, and probably 

 represents a very ancient impress of certain factors that developed at the close 

 of the last glacial period. Along the eastern side of the continent this northern 

 or boreal life element is found to extend some distance to the south along the 

 higher ranges of the Appalachian Mountain system, similar conditions to those 

 prevaiHng in the north being present as a result of altitude. In Hke manner 

 many southern species intrude northward along the bottom-lands of river 

 valleys, so that the line of demarcation is everywhere quite irregular. In 

 eastern Pennsylvania a truly boreal condition is found only in isolated patches 

 on the higher portions of the Alleghanies, while a transition type prevails 

 throughout the lower ranges and is the essential feature of the entire Piedmont 

 Plateau. The collective animal life of this territory is known as the Alle- 

 ghanian fauna and is typically "transition" in its character, while the boreal 



* Merriam, C. Hart, M.D.: "The Geographic Distribution of Life in North America." Smith- 

 sonian Report, 1 89 1. 



