CALCAREOUS MANURES— APPENDIX. 279 



to health. If the prairie lands could by a miracle be suddenly and com- 

 pletely deprived of all their lime, the decomposition and waste in the air of 

 their putrescent matter, now held combined and harmless, would make 

 them as sickly as the western coast of Africa. 



Exceptions and apparent contradictions explained. 



Supposing these general causes to operate in the formation of prairie 

 lands, the least reflection will show that their power and effects will be 

 often greatly modified by other circumstances. It is well known that in 

 prairie regions, the borders of rivers and small streams are generally 

 clothed with trees. They are protected from the fires in some measure by 

 the dampness of the earth, and because low bottoms are more sheltered 

 from winds. The river also is a secure barrier against the flames, and 

 therefore always guards one of its banks, at least. Even the close neigh- 

 borhood of those exempted places, would diminish the violence of the 

 flames ; and spots abundantly calcareous, and lying high, might thus retain 

 their wood growth. It would require that the flames should pass over a 

 considerable space, and with a full supply of dry fuel, to acquire the requi- 

 site force and rapidity for producing destruction. Therefore the vicinity of 

 the wooded banks of a river would not probably be changed from wood- 

 land to prairie, by any fires driven by winds from the river. To produce 

 this eflfect, the winds which prevail in dry seasons must drive the flames 

 toivards the rivers, and downward between their forks. The existir)g state 

 of things on the borders of the Mississippi and Missouri (as I have been 

 told) accords well with this position. The north-west winds are generally 

 dry, and blow with great violence; and wherever their direction is between 

 the forks of streams and down their course, the prairie extends nearly or 

 quite to the water's edge. But streams running from the opposite slope of 

 the great valley, oppose the course and obstruct the effects of these fires — 

 and the easterly winds, which would bear on them in like manner as to di- 

 rection, are generally accompanie.l by rain. TJierefore, in the last situation 

 calcareous soils may retain their growth of trees, and in the former, soils 

 well constituted to nourish and support them, may be brought to the state 

 of poor prairie land. 



If these general views are well founded, the manner in which prairies are 

 formed can no longer be mistaken; and though a highly calcareous soil is 

 deemed the most general and the most important means, the theory serves 

 as satisfactorily to explain the existence of prairies on various other situa- 

 tions, though the soil be. not calcareous. 



Ancient prairie lands in the lime-stone region of Virginia. 



In the foregoing observations I have limited the total absence of prairies 

 in the Atlantic states to the eastern slope from the mountains to the sea, 

 and to all poor land even among the mountains. In the rich limestone 

 lands of Rockbridge and Clarke counties, and perhaps on similar soils else- 

 where betsveen the Blue Ridge and Alleghany mountains, there certainly 

 were prairies at an early period. "When that part of Virgmia was first 

 settled by the present race of inhabitants, large bodies of land were covered 

 entirely bj'- young sapling wood, and there were other indisputable proofs 

 that at an earlier time kv^ trees, if any, had been there growing. But 

 though these lands are enough impregnated with lime (in some form) to be 

 very rich, and to be favorable to the growth of grass, they contain no car- 



