DELAWARE VALLEY ORNITHOLOGICAL CLUB. 17 



and New Jersey, where the slope is steeper and the conditions 

 more contrasted than in the south. In the case of free-moving 

 animals, notably birds, many Carolinian forms have easily 

 crossed it and are continually pushing further and further to 

 the north, where deforestation and resulting climatic changes 

 makes this possible.' Another interesting fact is that of the 

 Rose-breasted Grosbeak, an Alleghanian species, breeding at 

 Haddonfield^ and at Beverly, N. J.,' which, as Mr. Stone ob- 

 serves, ' ' is exactly parallel to the occurrence of upland plants 

 from Trenton down to Camden in West Jersey." 



The significance of the fall-line, as a barrier to the northward 

 extension of certain Carolinian species, seems to involve a differ- 

 ence in soil-formation affecting character of vegetation rather 

 than any question of temperature, for the elevation of the up- 

 land is not more than one hundred feet above the lowland. 

 The soils of the weathered crystalline gneisses of the upland are 

 loose compared with the stiff, compact clays which fringe its 

 foot. 



The fact is not that these Carolinian species could not find 

 favorable conditions in the upland section, but that they are 

 part of an ancient biotic condition that has not advanced be- 

 yond this line. That there is a tendency to advance on the 

 part of certain birds and trees there is no doubt, for we find an 

 invasion of Carolinian types into such areas as the lower Con- 

 necticut Valley, where conditions, probably as a result of the 

 old estuarine soils, offer favorable habitats. The Sweet Gum 

 Tree and the Worm-eating and the Blue- winged Yellow Warblers 

 are instances of this more northward dispersal beyond the ordi- 

 narily accepted limits of the fauna. Such species, likewise, in- 

 vade the upland districts above the fall-line along the numerous 

 streams that empty into the Delaware from the west. A fact 

 also of some note is the abundance of winter bird-life on the 



'See a paper by the writer on " The Geological and Geographical Relations 

 of the Land Bird Fauna of Northeastern America." The Auh, Vol. xxvi, 

 No. 3, July, 1909. 



^Abst. Proc. D. V. O. C, iii, p. 10 (Moore). 

 "uluA, 1897, p. 323 (Reed). 



