162 NezvYork State Museum 



2 Allegheny River Valley 



(Figure 26) 



The bottomlands of the Allegheny valley offer a wide 

 variety of studies in plant associations. There is a limited 

 number of trees, shrubs and herbaceous plants which are 

 common to the entire region and which may be found 

 both in the Allegheny valley and in the uplands of the 

 park area, but in general the flora of the valley is in 

 striking contrast to that of the higher valleys and slopes. 



During the glacial period or toward its close, an im- 

 mense quantity of material, chiefly gravels and sands, 

 evidently also some clay, was washed into the valley from 

 the southern edge of the glacial ice, which formed an 

 irregular semicircle around the northern edge of the 

 present valley. The depth of this deposit is unknown, but 

 certainly extends well below the present level of the river. 

 Since the close of the glacial period the Allegheny river 

 has cut its channel through this material to a depth of 

 25 to 50 feet, leaving much of the deposit in the form 

 of terraces or benches of various levels. The highest 

 benches are against the sides of the valley and the soil 

 conditions on them is of the most sterile and acid nature 

 to be found in the region. While mostly very dry there 

 are places where some moisture seeps up through the 

 deposits. 



The lower terraces are more moist, and in some places 

 where the surface is not well drained, very swampy woods 

 occur. In other places there has been in times of very 

 high water a deposition of some alluvial material by the 

 river. These areas support a luxuriant thicket vegetation. 

 Along the lowest levels there are occasionally found old 

 channels of the river which have been cut off from the 

 main stream and remain more or less filled with water 

 forming bayous, as at Cold Spring. 



