318 Annals of the Carnegie Museum. 



One aspect, an autumnal one, is to be noticed in this formation, 

 characterized by Soiidago nemoralis and Aster ericoides, constituting 

 together the So/idago- Aster Society. This society is mainly confined 

 to the younger portion of the sand-plain, being better developed in 

 that portion of the plain to the south and reachfng its best de- 

 velopment in the finer soil south of the Fog Whistle. As compared 

 with the Soiidago netfioralis growing so abundantly on the hills in the 

 vicinity of Pittsburgh the plants referred to that species on Presque 

 Isle are considerably smaller and have much lighter-colored leaves. 



The ArctostapJiylos-Juniperus Heath Formation. 



That part of the sand-plain fronting the northern part of Fong 

 Ridge has soil of a somewhat different character from that of the cor- 

 responding part of the sand-plain, as it is being formed to-day from the 

 beaches north of the Key Post. This older portion near Fong Ridge 

 has a less porous, more compact soil, owing probably in large part 

 to the drifting in of finer particles of sand by the wind, and in part 

 to the agencies of atmospheric disintegration, especially expansion 

 and contraction during the sudden extremes of temperature, to which 

 the sand-plain is exposed, this finally resulting in a splitting up of the 

 gravel into finer particles and at the same time rendering more avail- 

 able a certain amount of mineral plant-food. There is also some 

 humus to be seen in the upper layer of sand where the vegetation has 

 more nearly approached a closed formation. The accumulation of 

 humus is of necessity very slow in such a soil ; the scanty plant- 

 covering, the great porosity of the soil, the exposure to strong air 

 currents, and the great extremes of temperature through which the 

 soil passes, all tending to both prevent the accumulation of humus and 

 the retention of the products of the scanty humification. 



The habitat of the Arctostaphylos-Juniperus heath at present com- 

 prises the western portion of Fong Ridge, extending east from the 

 immediate vicinity of the Fight House for approximately a mile, and 

 also covering adjoining portions of the former sand-plain along the 

 northern side of the Ridge. The term " heath" is here used in the 

 sense employed by several American workers to indicate a xerophytic 

 formation characterized by evergreen shrubs. ^^ Cowles, referring to 



•"^^Cowles, H. C. /. c. Bot. Goz., 27: 367-369, May, 1899; Cowles, H. C. 

 /. c, Bot. Gaz., 31 : 173-174, March, 1501 ; Brown, ¥. B. H, "A Botanical 



