186 Journal of the Mitchell Society [March 



The passage from one forest type to another is seldom abrnpt, 

 but usually there is a g-radual transition, as that which accompanies 

 (1) difference in altitude; (2) variation in drainage, as when the 

 mountain slopes are ascended; or (3) change in the physical texture 

 of the soils, where the soils are residual and have been more or less 

 transported and difference in available moisture results. The most 

 abrupt transition from type to type within a short distance is usually 

 that which is due to difference in insolation, between north and south 

 slopes (Appendix 8), especially when the slopes are steep, or that 

 which results from marked differences in soil composition, especially 

 that between residual soils from the weathering in situ of calcareous 

 rocks (and still containing enough lime to render them alkaline or 

 neutral) (Appendix 9), and contiguous soils derived from a country 

 rock deficient in lime or potash, 



111 the eastern prevailingly gneissic, metamorphosed and foliated 

 division of the Appalachians, there is no definite stratification of the 

 country rock, and the forest types occur characteristicall}- in patches. 

 In the Alleghanies, on the other hand, where there is not only definite 

 stratification but great difference in the character of the country 

 rock — soft limestone, cherty limestone, clay shale, sandy shale, sand- 

 stone and quartzite alternating and the extremes often being in juxta- 

 position — the types are prevailingly in horizontal zones along the 

 slopes of the long ridges trending northeast and southwest which 

 characterize the Alleghanian structure, the zonation of the types 

 due to stratification of soils being interrupted by surface configura- 

 tion, where minor valleys and hollows indent the slopes. 



The facies of the mixed type (society) can often be separated into 

 two groups of species: That portion of it which is formed of species 

 each of which constitutes more than 20 per cent of the stand, con- 

 trolling speci&s, and the minor species each of which forms less than 

 20 per cent though more than 5 per cent of the mixture. Locals 

 are species of limited distribution and while within a limited area 

 they may be abundant in a type, they do not form a general feature 

 in it throughout its entire distribution (Cladrastis tinctoria, Bohinia 

 viscosa, Magnolia macrophylla, Tsuga caroliniana) . Locals may be 

 species in the formative stage or they may be relics of species possi- 

 bly once of wide distribution which have become nearly extinct. 

 Vagrants are species of wide distribution entering possibly many 



