Prairies, Flats, and Barrens in Southern Illinois. 389 
my theory. For example, the grass-covered bottoms of former 
of western Utah, where whole mountain ranges are covered 
with sharp angular fragments of rocks, undecomposed for lack 
of moisture. Little soil could thus be formed on these slopes, 
which therefore produce but a scanty vegetation, while there isa 
most luxuriant growth of delicate flowers at the same altitude 
on every little rivulet trickling down from the snow-clad sum- 
mits, and even on the moist patches of soil under and between 
the melting banks of snow. In other regions, again, the absence 
of trees and the general barrenness of the country seem to be 
due to an excessive accumulation of various salts in the upper 
erust of the soil, such as sulphate of magnesia, chlorid of sodium, 
carbonate of soda, and others, but which accumulate also in conse- 
quence of the insufficient drainage, due to the small amount of 
atmospheric precipitation 
the spring, whereby all but the hardiest grasses were destroyed, 
and those especially remained which propagate by throwing ran 
ss 
