SOIL. 



taiiiing eleven parts out of twelve fand. Any much greater 

 proportion of fand, however, it is ftated, always produces 

 abfolute fterihty. The foil of Baglhot-Heath, which is 

 wholly devoid of vegetable covering, contains, it is faid, 

 lefs than one-twentieth of finely divided matter ; 400 parts 

 of it, which had been heated red, afforded the above writer 

 380 parts of coarfe fiHceous fand, 9 parts of fine fand of 

 the fame kind, and 1 1 parts of impalpable matter, which 

 was a mixture of ferruginous clay, with carbonate of lime. 

 Vegetable or animal matters, when finely divided, not only 

 give, it is faid, coherence, but likewife foftnefs and pene- 

 trabihty ; but neither they, nor any other part of the foil, 

 Hiuft be in too great proportion ; and a foil is unproduftive, 

 if it confifts entirely of impalpable matter. Pure alumina or 

 filica, pure carbonate of magnefia, are incapable of lup- 

 porting healthy vegetation. And no foil is fertile, it is 

 itated, that contains fo much as nineteen parts out of twenty 

 of any of the conftituent materials that have been mentioned 

 above. 



In anfwer to the important queltion, whether the pure 

 earths in the foil only aft in a mere mechanical manner, or 

 as indireft chemical agents, or aftually furnilh the food of 

 the plants ? it is itated, that as their bafes have not yet 

 been decompofed, there is no reafon to fuppofe that they 

 are capable of being converted into the elements of or- 



fanized compounds, as into carbon, hydrogen, and azote, 

 lants have been made to grow, it is faid, in given quantities 

 of earth, but they confume very fmall portions only ; and 

 what is loft may be accounted for, by the quantities found 

 in their alhes, that is to fay, it has not been converted into 

 any new produfts. The carbonic acid united to lime or 

 magnefia, if any ftronger acid happens to be formed in the 

 foil during the fermentation of vegetable matter, which will 

 difengage it from the earths, may, it is faid, be decom- 

 pofed ; but the earths themfelves cannot be fuppofed con- 

 vertible into other fubftances, by any procefs taking place 

 in the foil or land. In all cafes, the afhes of plants, it is 

 obferved, contain fome of the earths of the foil in which 

 they grow ; but thefe never equal more than one-fiftieth of 

 the weight of the plant which is confumed. On the whole, 

 it is concluded, that if they be confidered as neceffary to 

 the vegetable, it is as giving hardnefs and firmnefs to its or- 

 ganization. Thus wheat, oats, and many of the hollow 

 grafles, have, it is faid, an epidermis principally of filiceous 

 earth ; the ufe of which feems to be to ftrengthen them, 

 and defend them from the attacks of infefts and parafitical 

 plants. 



It is ftated that, for the moft part, the foils, the con- 

 ftituent materials of which are the moft various and con- 

 trary to each other, are thofe of the alluvial kind, or which 

 have been formed in a gradual manner from the depofi- 

 tions of rivers, or other waters : they are, in many cafes, 

 extremely fertile. The writer juft mentioned has examined 

 fome produftive foils of this fort, which have been very 

 different in their compofition. A very productive foil from 

 the banks of the river Parrot, in the county of Somerfet, 

 afforded eight parts of finely divided earthy matter, and 

 one part of fiUceous fand : the analyfis of the former gave 

 thefe refults : 



360 parts of carbonate of lime, 

 25 parts of alumina, 

 20 parts of filica, 

 8 parts of oxyd of iron, 

 19 parts of vegetable, animal, and faline matter. 



A rich foil of this nature from near the Avon river, in 

 the valley of Evelham, in the county of Worcefter, gave 



three-fifths of fine fand, and two-fifths of impalpable mat- 

 ter : the latter confilled of 



35 Alumina, 



41 SiHca, 



14 Carbonate of lime, 



3 Oxyd of iron, 



7 Vegetable, animal, and faline matter. 



From a fpecimen of good foil of Tiviotdale, five-fixths 

 of fine fihceous fand, and one-fixth of impalpable matter, 

 were afforded : the latter confifted of 



41 Alumina, 



42 Silica, 



4 Carbonate of lime, 



5 Oxyd of iron, 



8 Vegetable, animal, and faline matter. 



And a foil affording excellent pafture from the valley of 

 the Avon, near the town of Sahfbury, gave one-eleventh of 

 coarfe fihceous fand ; the finely divided matter of which 

 confifted of 



7 Alumina, 

 14 Sihca, 

 63 Carbonate of lime, 



2 Oxyd of iron, 

 14 Vegetable, animal, and faline matter. 



It is ftated that, in all thefe cafes, the fertility feeraed to 

 depend upon the ftate of divifion and mixture of the earthy 

 materials and the vegetable and animal matters ; which may 

 be readily explained from what has been already advanced. 



And profeffor Davy, in fpeaking of the improvement of 

 foils, as connefted with the principle of their compofition, 

 remarks in the paper noticed above, that when a barren 

 foil is examined with a view to its improvement, it ought, 

 in all cafes, if poflible, to be compared with an extremely 

 fertile foil in the fame neighbourhood, and in a fimilar fitua- 

 tion : the difference given by their analyfes would indicate 

 the methods of cultivation ; and thus the plan of improve- 

 ment would be founded upon accurate fcientific principles. 

 And that, if the fertile foil contained a large quantity of 

 fand, in proportion to the barren foil, the procefs of ame- 

 lioration would depend fimply upon a fupply of this fub- 

 ilance ; and the method would be equally fimple with re- 

 gard to foils deficient in clay or calcareous matter. But 

 that in the apphcation of clay, fand, loam, marie, or chalk 

 to lands, there are no particular chemical principles to be 

 obferved ; but when quicklime is ufed, great care muil be 

 taken that it is not obtained from the magnefian Umeftone ; 

 for in this cafe, as has been fhewn by Mr. Tennant, it is 

 exceedingly injurious to land. The magnefian hmeftone 

 may be diftinguifhed from the common limeftone by its 

 greater hardnefs, and by the length of time that it requires 

 for its folution in acids, and it may be analyfed by the pro- 

 cefs for carbonate of hme and magnefia. When the ana- 

 lytical comparifon indicates an excefs of vegetable matter 

 as the caufe of fterility, it may be deltroyed by much pul- 

 verization, and expofure to air, by paring and burning, or 

 the agency of lately made quickUme. And the defeft of 

 animal and vegetable matter mult be fupplicd by animal or 

 vegetable manure. 



And it is further ftated, that fterile foils in different cli- 

 mates and fituations muft differ in compofition. The gene- 

 ral indications of fertility and barrennefs, as found by che- 

 mical experiments, muft iieceflarily differ in different cli- 

 mates, and under different circumftances. The power of 

 foils to abforb moiiture, a principle effential to their pro- 



duAivenefs, 



