Current Literature 69 



The underlying rock is sandstone and conglomerate. Owing to 

 the differential erosion of these rocks, numerous caves, canyons 

 and gullies are formed. The coldness of these places, accentuated 

 by the slow melting of accumulated snows in the spring, makes 

 them a congenial habitat for many northern plants which here 

 find their southern limit. Since the region lies below the boun- 

 dary of glacial drift, the soils except in the stream valleys are 

 residual, varying from light clay to pure sand. 



With respect to the forests of the region, we find that the bot- 

 tom lands may contain Red maple swamps in pure stands or mixed 

 with elm in the damper situations ; in the drier situations, the 

 maple is associated with Pin oak. Swamp White oak and Shingle 

 oak, or with both species of Juglans, Red ash and White ash. On 

 certain limited areas one may find Yellow birch. Sweet birch and 

 River birch growing together in the stream bottoms. The heav- 

 iest forests are hemlock, which are most luxuriant along the lower 

 slopes and bottoms of the deepest ravines. Sweet birch is often 

 mixed with the hemlock, and the forest floor is frequently car- 

 peted with yew. A liriodendron forest flourishes in conditions but 

 little different from those of the hemlock forest which it is replac- 

 ing. The forest in which the tulip dominates is richer in number 

 of species than any of the others ; among the most abundant are 

 chestnut, hemlock, butternut and beech. 



Proceeding back from the edge of the cliffs, one finds first a 

 lichen tundra in miniature, then a zone of pine (P. rigida and 

 P. virginiana) , and finally an oak forest where the ridges become 

 wider and the soil deeper. The oaks are Chestnut oak, White oak 

 and Black oak. With them are frequently associated chestnut 

 hickory, Sour gum and Red maple. These two types of the upland 

 forest are the extremes between which are all intermediates and 

 the various intermediates make up most of the upland forest. 



The book is illustrated by photographic reproductions much 

 above the average in quality, especially in showing detailed struc- 

 ture of the various plant habitats. 



C. D. H. 



