78 BIG SPRING PRAIRIE. 
about all of the trees upon the newly occupied area. 
Upon most of this area between the depressions repre- 
sented on Map II, numerous young trees of Populus 
deltoides (Cottonwood); Populus tremuloides (Trem- 
bling Aspen); and Ulmus americana (American Elm), 
were gaining a foothold. 
One of the clay islands in the western part of the 
prairie contains only Elms. The other clay islands or 
clay banks represented exhibit slight variations in the 
relative number of the species enumerated above, but 
all of the species are characterized by the prominent or 
exposed roots. 
Fig. 17 represents a peculiar formation of a Maple 
tree which occurs a short distance southwest of one of 
the clay islands in the western part of the prairie. The 
clay-bed gradually sloped from the island in either 
direction. After drainagea seedling maple sprang up 
and flourished for several years. As the muck is 
deeper here than on the island, the tips of the larger 
roots only were imbedded in the clay; asa result the 
tree could not successfully withstand the strong wind 
to which it was exposed. When it was blown down, 
the roots were not broken off as commonly happens, 
when they are imbedded in hard soil. The roots on 
the windward side were torn loose, and have decayed 
as can be noted by a careful inspection of cut. 
Those on the side nearest the prostrate trunk were 
but little disturbed. Hence the tree continued its 
growth, The principal branches survived in their 
struggle for existence, the other branches being shaded 
gradually decayed, and the resulting formation ensued. 
This is an apt illustration of a successful struggle for 
existence under adverse conditions. ‘The illustration 
shows in the back-ground another tree not so suc- 
cessful in its struggle. The mere looseness of soil on 
prairie where muck is quite deep may be sufficient 
reason to account in part for the absence of trees of any 
size on such areas. 
