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on which the forest is mainly Black Oak and Scarlet Oak, with quite a mixture 
of other species. There is very little of this forest left undisturbed in the district 
owing to its desirability both for agricultural purposes and, in the neighborhood 
of the cities, for residential purposes. The altitude is about 900 feet above the 
sea and much of the best residential section of Pittsburgh Is located here. The 
mosses are evidently about the same species as those listed under “5,” being 
mainly those confined to logs, humus, or bases of trees. 
5. Betula-Acer-Fagus-Quercus Association. Birch-Maple-Beech-Oak Forest. 
Below the gorge, where the stream is eroding most rapidly, the valley widens 
out and, eventually, there result more or less gentle slopes, broken up here and 
there by side ravines and by landslides, or here and there under-cut by the 
stream, which may be beginning to meander in the widening flood-plain. The 
forest is a difficult one to briefly characterize. The nature of the slopes varies 
in steepness and in exposure, and this is to a measure expressed in the varying 
vegetation. In general the most prominent trees are the Cherry Birch, Red 
Maple, Beech, and Black Oak, with here and there a prominent mixture of Red 
Elm, Black Cherry, Locust, Sour Gum, White Ash, Tulip Tree, Basswood, and 
White Oak. The soil is usually quite unstable, always working down slope and 
thus often being a mechanical mixture of stones, clay, decaying leaves, sticks, 
etc. The moss flora of this forest is better developed than that of any of the 
other habitats: 
A. Shaded clay soil on slopes. 
Campylium chrysophyllum (Brid.) Bryhn. 
Catharinaea angustata Brid.* 
Catharinaea undulata [L.] W. & M.* and var. allegheniensis Jenn.* 
Dicranella heteromalla [Dill.] Schimp. 
Ditrichum pallidum [Schreb.] Hampe. 
Ditrichum tortile [Schrad.[ Brockm. 
Mnium cuspidatum L., Hedw. 
Physcomitrium turhinatum (Rich.) C. M. 
Weber a nutans [Schreb.] Hedw. 
B. Woods humus or humus-covered soil on shaded slopes. 
Amblystegium Kochii Bryol. Eur. 
Mnium cuspidatum L., Hedw.* 
Plagiothecium denticulatum [L.] Bryol. Eur.* 
Plagiothecium sylvaticum [Huds.] Bryol. Eur. 
Platygyrium repens [Brid.] Bryol. Eur. 
Rhynchostegium serrulatum (Hedw.) Jaeg.* 
Stereodon imponens (Hedw.) Lindb.* 
Stereodon Haldanianus (Grev.) Lindb. 
Thuidium delicatulum [L.] Mitt.* 
C. Logs on shaded slopes. 
Brachythecium acuminatum (Hedw.) Kindb. 
Brachythecium campestre (Bruch) Bryol. Eur. 
