342 Annals of the Carnegie Museum. 



dendron and the heath as there is on the sand-plain between the Myrica 

 thicket and the heath. The pure heath-formation extends farther 

 inland along Long Ridge than it does on the sand-plain, showing here 

 its greater adaptability to positions of greater exposure. 



The Pinus Strohiis and Quercus vehitina Forest-formations 



(on ridges). 



The heath on Long Ridge passes into the Pinus Strobus forest and 

 finally into the Quercus velutina forest, as does also the heath on the 

 sand-plain. A typical example of the white pine forest occurs on the 

 older arm of Long Ridge extending to the southwest of the Light 

 House. The fine black oak forest at the western end of the ridge near 

 Jetty No. 2 and on the two ridges between ridges No. 2 and No. 3, 

 probably occupies the site (at least partially) of a former white pine 

 forest. As has been seen, the last mentioned ridges are probably be- 

 tween five hundred and six hundred years old, and, from what can be 

 deduced from known facts, it is probable that the portions of these 

 ridges which constituted the habitat of the white pine forest have been 

 largely washed away. 



The Pruuus Forest- formation (on ridges). 



The Toxicodendron thicket, like the Myrica thicket, accumulates 

 vegetable debris quite rapidly and with the consequent increase of 

 humus conditions becomes suitable for other species. The succeeding 

 formation is practically the same as that following the Myrica thicket ; 

 the Prunus forest-formation. About the only difference noted was 

 the greater abundance of lianes ; Celastrus, Vitis, Psedera {Parthetw- 

 cissus) and Sinilax, and the absence oi Alnus and Acer. Prunus vir- 

 giniana is more abundant in the early stages of the formation, and 

 there are usually a few old cottonwoods, relicts of the earlier formations. 



The Prunus forest-formation on ridges is relatively short lived and 

 soon gives way to the Quercus velutina forest. Portions of the ridge 

 between the Board Walk and Big and Graveyard Ponds are occupied 

 by the Prunus forest, but much of this area, has evidently been burned 

 over, and is now occupied by a secondary burn succession. 



The Quercus velutina Forest-formation (on ridges). 



The Quercus velutina forest-formation succeeding the Prunus forest 

 is at its best on the ridges between Long and Big Chimney Ponds. 



