18 College of Forestry 
and, on the other hand — and this is of particular interest 
to us — what changes have been wrought in the environment 
by vegetation? As between these two aspects of action and 
response — between vegetation and environment — no doubt 
the latter has the greater significance for us (the people of 
New York), for we are especially concerned for example 
with the character of our soils, and it is upon the soil environ- 
ment that vegetation works the most profound modifications. 
Landmarks of Development. 
Two landmarks in history, the one geologic, the other of 
human history, will serve to measure the development of 
vegetation in the particular meaning employed in this bulle- 
tin, and equally well to show the work done by vegetation 
in modifying the character of the surface of this State — 
especially as to soil building. The first landmark covers a 
space of geologic time at the close of the glacial epoch, when 
the encroaching ice-cap having obliterated the plant life of 
the area covered by it (including all of New York State 
except a coastal strip of Long Island and a small area in the 
southwest), the retreating glacier — 1. e., the melting of the 
vast ice sheet — deposited its enormous load of debris, the 
soils, sand, gravel, boulders, all the sediments of rock deca 
and agmentation, of debris of every sort caught up in the 
forward flowing clediens. The olacial waters further affected 
the sorting and deposition of this debris, and while this work 
of erosion, carrying and deposition is always going forward, 
still we may imagine a time when the elacial recession left 
its finished product —the foundation structures of our 
State, mountain and valley, plateau and plain covered to a 
greater or less depth by glacial debris, or areas of rock 
polished and left bare by ice action with its scouring tools, 
i. e., the sand, gravel, etc., held in the ice mass. As a 
plowed landscape hes ready for the natural reseeding by 
plants, so this vast and diversified terrain lay open to re-inva- 
sion by vegetation. The return of vegetation would confront 
the problems of establishing a plant cover upon bare rock, 
