14 , PROCEEDINGS OF THE 



more northern cities, a ship-way to the sea. In southeastern 

 Pennsylvania this "upland terrace" is marked on survey maps 

 by the 200-foot contour. Fox Chase, the escarpment at Wayne 

 Junction, George's Hill in Fairmount Park, Swarthmore Col- 

 lege and the Chester Reservoir are some of the well-known 

 points along this overlook. The Baltimore "Pike" follows 

 along the brow of this terrace from Clifton Heights to Swarth- 

 more. 



Now this same fall-line has, to the student of animal and 

 plant distribution, another and an exceedingly interesting sig- 

 nificance in that it marks, or has long been supposed to mark, 

 in its northern portion, a boundary line between two faunal 

 areas — the Carolinian and the Alleghanian. Two important 

 lines of thought present themselves in considering this faunal 

 frontier. What relation does the distribution of living beings, 

 thus limited in their northward spread, bear to the geological 

 history of the land area in question, and, secondly, does this 

 topographical feature in reality possess the qualities of a barrier? 



From all the evidence that exists in its topography and in the 

 nature of its deposits there is little doubt that the present coastal 

 plain was, in comparatively recent times, a submerged landward 

 strip of the continental shelf, the greater portion of which still 

 lies beneath the marginal waters of the Atlantic, stretching east- 

 ward for some two hundred and fifty miles from the Upland 

 terrace (fall-line) to the 100-fathom line, where it slopes ab- 

 ruptly down into the deep basin of the ocean. The whole 

 width of this shelf is quite uniform from north to south, but in 

 the northern portion the submerged area is far in excess of the 

 exposed part that now forms a narrow coastal plain. The de- 

 posits of this strip of land are of the Tertiary and Quaternary 

 Age, and the uplift probably took place slowly during the late 

 Pliocene and the early Quaternary, 



The history of the Carolinian fauna appears to be intimately 

 related to this coastal-plain formation. As the area became an 

 exposed land-surface a gradual spread of forest-growth took 

 place wherever soil-conditions were favorable, the several domi- 

 nant types of plant-associations occupying districts best suited 

 to their peculiar physiological needs. The more or less uniform 



