60 College of Forestry 
forest elements persist more or less strongly to Glens Falls 
and Whitehall. These forest forming species follow the 
drainage valleys of the Delaware, Susquehanna and Alle- 
ghany systems well into the Alleghany plateau, 1. e., into the 
zone of sugar maple, hemlock, white pine, beech and yellow 
birch. This northerly extension appears to be especially 
marked in the region where the long, deep valleys of the 
Cayuga and Seneca lake basins continue the dissection across 
the plateau into the Ontario basin. 
The case of Keene Valley above mentioned seems properly 
to be explained on the ground of a north-south cleft along 
which more southerly species extend into otherwise character- 
istic Adirondack conditions. Naturally these north-south 
channels give rise to the so-called “‘ warm pockets” where 
natural species exist or cultivated ones thrive which could 
not endure the temperature conditions (early and late frosts 
probably) of the general region. No doubt numerous such 
warm pockets are known to farmers and fruit growers al- 
though I have not gathered the data concerning them. 
Kaaterskill clove (see frontispiece) is a cleft opening south- 
ward from the Catskills upon the Hudson Valley. Here the 
oak, chestnut, hickory zone (notably chestnut-oak in force) 
is thrust up beyond 1500 feet elevation into the sugar maple, 
yellow birch, beech, white pine, hemlock zone on the border 
of a yet more boreal expression of it as indicated by red 
spruce and balsam (at 2000 feet). 
On the other hand, these same north-south channels cut in 
the Alleghany plateau, appear to favor the extension of 
boreal species southward beyond their general New York 
range. This phenomenon is associated with the exposure by 
dissection of high steep north and east cliffs and slopes. 
Without the support of experimental data or frost records 
one would say that we are here dealing on a large scale with 
a difference like that between the sunny side and the shady 
side of a house standing in the open. Such a case is found 
on a north facing wall of the Genesee gorge at Letchworth 
Park where paper birch and red pine are present. The val- 
