SOIL. — ITS FORMATION AND COMPOSITION. 



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acconut of tho leading formations. I shall commence with 

 the consideration of the granitic rocks. 



1 20. jjE^NiTE^as we have seen, covers a large space in this 

 country; it composes also nearly the whole of Scotland, north 

 of the Grampians. It contains nearly all the ingredients which 

 plants require, but some of them in exceedingly small quan- 

 tity. It is conrpo?^o,d of thrift minerals, quartz^. 

 feldspar \ and OQcasiojiallj in some of the mountains described ' 

 as granite, a mineral named ho rnblende , takes the jilacfiof 

 mica, which, as it possesses considerable difference of composi- 

 tion, must materially influence the character of the soil 

 derived from this rock. Mica, feldspar, and hornblende pos- 

 sess the following composition in the hundred parts. 



IMica. Feldspar. Hornblende. 



121. From the variety of composition which granite ex- 

 hibits, the character of its soils may be expected to vary. 

 Though in the North of Scotland and in the West of Ireland 

 granite soils being usually elevated, are regarded as most 

 unproductive, yet industry can render them capable of yielding 

 food, for on the lofty summits of the Wicklow mountains, 

 1600 feet above the level of the sea, splendid crops of 

 turnips and flax are produced. The deficient ingredients 

 in granite are phosphoric acid and lime, and accordingly the 

 farmers in Moume and the agricultural improvers in other 

 granite districts find that, by the application of lime, or of 

 bones, which contain both lime and phosphoric acid, they 

 can procure excellent crops of oats and wheat (see manures), 



• These minerals may be distinguished by the following characters: — 



Quartz or Silica occurs usually crystallized in granite. It will scratcli 

 ^'lass ; a knife will not scratch it, but produces a streak like that made 

 l)y a lead pencil. 



Mica is of various colours; it occurs of a yellow colour in the Dublin, 

 and of a black in the Newry granite. It is met with in shining scales, 

 which split into layers when heated in the flame of a candle, and arc so 

 soft that they can be cut with a knife. 



Feldspar, the next ingredient of granite, forms a large portion of it.s 



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