American Association at Dubuque. 289 
other, or into both from a common source, but in abiding there. 
The primordially unbroken forest of Atlantic North America, 
nourished by rainfall distributed throughout the year, is widely 
separated from the western region of sparse and discontinuou 
tree-belts of the same latitude on the western side of the con- 
tinent, where summer rain is wanting or nearly so, by immense 
treeless plains and plateaux of more or less aridity, traversed 
by longitudinal mountain ranges of a similar character. Their 
other lands, are mostly southward, on the Mexican plateau, or 
Many as far south as Chili The same may be said of the 
Plants of the intervening great plains, except that northward 
