CALCAREOUS MANURES— APPENDIX. 277 



little lime, as to be, if not naturally poor, at least unfriendly to the growth 

 of grass. Hence such lands are covered naturally by an unmixed growth 

 of trees, and are almost destitute of grass. Calcareous soils are, on the 

 contrary, favorable to the growth of grass, and unfavorable to the growth 

 of trees, and the more so (other circumstances being alike) in proportion to 

 the excess of lime in the soil. Supposing such a soil to have been so pro- 

 tected as to be covered with trees, the first passage over it of fire, which 

 would be harmless to the more hardy growth of acid soil, would here serve 

 to scorch and damage the trees, feeble and tender, because unnaturally 

 placed. This effect would be the greater because such calcareous wood- 

 land would have some growth of rank grass, which, as dry fuel, Would add 

 to the violence of the fire, and to its effect. The next winter, the crippled and 

 stinted condition of the trees would prepare them to be still more damaged 

 by the like passage of fire, and its violence would be increased by the greater 

 quantity of dead and dry wood, and the increased growth of grass less ob- 

 structed now by shade. Every year these circumstances would serve the 

 more to augment the destructive power of the fires, and to diminish the 

 power of resistance in the still living trees. In the course of time all the trees 

 would be killed, and burnt, and then the seeds and roots after springing in 

 vain many succeeding summers, would finally have to yield to destruction 

 also. The surface is then covered with the grov/th of grass most suitable 

 to its composition, which grov/th is luxuriant according to the fertility of the 

 soil. So long as fires sweep every year over such land, the prairies can 

 never be covered with wood; and on the contrary will be extending every 

 year so long as there is wood which the fires can destroy, and land that 

 will yield grass to furnish the fuel for still more extended ravages. 



It may well happen also, that a soil not at all calcareous, if bordering on 

 a prairie, would be so exposed to the power of fire, when driven in all its 

 violence by strong winds, that its trees would be damaged, and finally 

 killed, and the land brought likewise to the prairie state. Such land, however, 

 would be making continual efforts to return to its more natural state of 

 wood-land ; and whether under young wood, or a meager cover of grass, 

 would, by refusing fuel, serve to check the farther extension of the ravages 

 of fire. 



This would be one means of land not calcareous being brought to the 

 prairie state. There are two other means for the formation or extension of 

 prairies on land not calcareous, both of which are probably more often 

 operative. These will now be considered. 



It may be inferred that the destruction of trees on calcareous S'ils is not 

 so much caused by their absolute unkindliness to trees, as by their far 

 greater suitableness for grass, which serves when dry as fuel to burn the 

 trees. Now if any thing other than the presence of calcareous earth will 

 produce an equally rank growth of grass, the same destructive end will be 

 produced, and as completely in time, though perhaps with less facility and 

 quickness. Moisture in the soil will in this manner serve as well as calca- 

 reous matter— and if the surface is only dry enough at sometime in every 

 year to permit full force to the fire, similar effects must be produced in de- 

 stroying and keeping down the growth of trees. In this manner are formed 

 the rich alluvial prairies or savannas on the great western rivers, which are 

 covered by floods sometimes, and perfectly dry at others. 



Again— a soil may be free from floods, and from all water except from 

 the clouds, and yet without being calcareous, may be so constituted as to 

 attract and retain moisture, with great force, and thus be very favorable to 

 the growth of grass, and consequently to the formation of prairies. This 

 constitution is produced when a soil is formed almost entirely of fine alu- 



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