2JJ4 CALCAREOUS MANURES-APPENDIX. 



sandy deserts and irrigated regions have been competent, and enough 

 observant, to describe the agricultural qualities of the soils. I have not 

 heard of there having been brought away any specimens of such remark- 

 able soils, except in a single case ; and for which one opportunity for obtaining 

 direct proof of the ingredients we are indebted to the enlightened curiosity 

 and investigating mind of an American lady. When I was lately (in 1842) 

 at tlie Patent Office in Washington, I saw among many other collected 

 subjects of curiosity, a small bottle labelled " Sand from the desert of 

 Barca." It had been obtained and was presented by Mrs. Macauley, the 

 wife of David S. Macauley, the American consul at Barca. I asked for and 

 obtained a small portion of it, for the purpose of ascertaining its com- 

 position in regard to calcareous matter. Upon trial I found it to contain 

 49 per cent, of carbonate of lime ; This sand is very fine, of a pale yellow 

 color, and would offer to the eye, or to slight observation, no indication of 

 being any thing else than almost pure silicious sand, slightly tinged by 

 ferruginous matter. 



It may seem to some readers that these speculations on sandy deserts, 

 upon such few data furnished in positive facts, are a wide departure from the 

 investigation of prairie soils; and that the deductions, even if established, 

 are more curious than useful, and can lead to no practical result. But it is 

 not so, if the lights thus obtained are properly applied. The facts here 

 presented in connexion with others previously discussed, serve to show 

 that the same cause, (a very large proportion of calcareous earth,) according 

 to the existence or changes of other circumstances, may produce in soils 

 either the highest degree of fertility, or the most complete sterility. These 

 modifying circumstances are the presence in the soil of much putrescent 

 matter, the accumulation of ages of repose under grass, or of abundance of 

 water — or of the absence or great deficiency of both. It may be merely a 

 matter of curious speculation, however correctly deduced from the positions 

 here maintained, that it is possible, and perhaps would be profitable, merely by 

 raising water to the surface, to bring to a state of productiveness most of 

 the naked and burning deserts of Africa. But another deduction is not 

 merely a matter for idle and amusing speculation, but is a most important 

 truth, and strictly applicable to practice ; which is, that the rich prairie 

 regions of the west and south-west of the United States and of Texas, if 

 continued to be scourged unremittingly by exhausting tillage, will finally 

 become deserts as barren as those of Lybia and Barca. 



