GENERAL REMARKS. 5 



forests. This treeless plateau extends north to the fifty-second degree of north latitude ; it follows southward the 

 trend of the Eocky mountains far into Mexico, extending eastward at the point of its greatest width, in about latitude 

 40 2f ., nearly to the ninety-seventh meridian. This whole region is generally destitute of forest. The narrow bottoms 

 of the large streams are lined, however, with willows, poplars, elms, and hackherries, trees adapted to nourish 

 under such unfavorable conditions. These diminish in size and number with the rainfall, and often disappear 

 entirely from the banks of even the largest .streams toward the western limits of the plateau, south of the forty-fifth 

 degree of latitude. North and east of these central treeless plains a belt of prairie extends from the sixtieth degree 

 of north latitude to southern Texas. The average width east and west of this prairie region, through much of its 

 extent, is not far from 150 miles. Its eastern extension, between the fortieth and forty-fifth degrees of latitude, is 

 much greater, however, here reaching the western shores of lake Michigan, and forming a great recess in the western 

 line of the heavy forest of the Atlantic region with a depth of nearly 000 miles. The transition from the heavy 

 forest of the eastern and central portions of the Atlantic region to the treeless plateau is gradual. The change 

 occurs within the prairie region. Here is the strip of debatable ground where a continuous struggle between the 

 forest and the plain takes place. There is here sufficient precipitation of moisture to cause, under normal conditions, 

 a growth of open forest, but so nicely balanced is the struggle that any interference quickly turns the scale. Trees 

 planted within this prairie belt thrive if protected from lire and the encroachment of the tough prairie sod, and so 

 extend the forest line westward ; if the forest which fringes the eastern edge of the prairie is destroyed it does not 

 soon regain possession of the soil, and the prairie is gradually pushed eastward. 



The eastern line of the plain where arborescent vegetation is confined to the river bottoms, and which divides 

 it from the prairie where trees grow naturally, to some extent, outside of the bottoms, and where they may be made 

 to grow under favorable conditions everywhere, is determined by the rainfall enjoyed by this part of the continent. 

 The extreme eastern point reached by this line is found, upon the fortieth degree of north latitude, near the northern 

 boundary of the state of Kansas. Xorth of the fortieth degree it gradually trends to the west, reaching the eastern 

 base of the Eocky mountains in about latitude 52. This northwestern trend of the eastern plain line may be 

 ascribed to the comparatively small evaporation which takes place during the shorter summer of the north and to 

 a slight local increase of spring and summer rainfall. South of the fortieth degree the plain line gradually trends 

 to the southwest under the influence of the gulf of Mexico, reaching its extreme western point in Texas upon the 

 one hundredth meridian. 



Other causes, however, than insufficient rainfall and a nicely balanced struggle between the forest and the 

 plain have prevented the general growth of trees in the prairie region east of the ninety-fifth meridian. The rainfall 

 of this region is sufficient to insure the growth of a heavy forest. The rain falling upon the prairies of Minnesota, 

 Wisconsin, Iowa, Illinois, and Missouri equals in amount that enjoyed by the Michigan peninsula and the whole 

 region south of lakes Ontario and Erie, while prairies exist within the region of the heaviest forest growth. It is 

 not want of sufficient heat, or of sufficient or equally distributed moisture, which has checked the general spread of 

 forest over these prairies. The soil of which the prairies are composed, as is shown by the fact thai trees planted upon 

 them grow with vigor and rapidity, is not unsuited to tree growth. It is not perhaps improbable that the forests 

 of the Atlantic region once extended continuously as far west at least as the ninety-fifth meridian, although, 

 circumstantial evidence of such a theory does not exist ; and the causes which first led to the destruction of the forests 

 in this region, supposing that they ever existed, cannot with the present knowledge of the subject be even guessed at. 

 It is, however, fair to assume that forests once existed iu a region adapted, by climate, rainfall, and soil, to produce 

 forests, and that their absence under such conditions must be traced to accidental causes. It is not difficult to 

 understand that the forest once destroyed over such a vast area could not easily regain possession of the soil 

 protected by an impenetrable covering of sod and subjected to the annual burnings which have occurred down to 

 the present time; while the force of the wind, unchecked by any forest barrier, over such an area would, even without 

 the aid of fires, have made the spread of forest growth slow and difficult. The assumption that these eastern 

 prairies may have once been covered with forests is strengthened by the fact that since they have been devoted 

 to agriculture, and the annual burning has been stopped, trees which were formerly confined to the river bottoms 

 have gradually spread to the uplands. Small prairies situated just within the western, edge of the forest have 

 entirely disappeared within the memory of persons still living ; the oak openings open forests of large oaks through 

 which the annual fires played without greatly injuring the full-grown trees once the characteristic feature of these 

 prairies, have disappeared. They are replaced by dense forests of oak, which only require protection from fire to 

 spring into existence. In western Texas, the mesquit, forced by annual burning to grow almost entirely below 

 the surface of the ground, is, now that prairie fires are less common and destructive, spreading over what a few 

 years ago was treeless prairie. The prairies, then, or the eastern portions of them situated iu the region of abundant 

 rainfall, are fast losing their treeless character, and the forest protected from fire is gradually gaining in every 

 direction ; regions which fifty years ago were treeless outside the river bottoms now contain forests covering 10 or 

 even 20 per cent, of their area. These eastern, well-watered prairies must not, however, be confounded with 

 their dry western rim adjoining the plains the debatable ground between forest and plain or with the plains 

 themselves. There is now no gradual, constant spread of forest growth upon the plains. They are treeless, on account 

 of insufficient moisture to develop forest growth; and while trees may, perhaps, if planted, survive during a few years 



