AGENCY OF THE RAINS AND WINDS. 427 



IX., § 1), which is gathered from beneath, wherever the roots pene- 

 trate, and is by them sent upwards to the surface. A ton of hay con- 

 t;ains about 170 lbs. of this inorganic matter (Lee. X., § 3). Suppose 

 the roots to contain as much, and that the total annual produce of 

 grass and roots together amounts to four tons, then about 680 lbs. of 

 saline and earthy matters are every year worked up by the living 

 plants, and in a 'great measure permanently mixed with the surface 

 soil. Some of this, no doubt, is carried off by the cattle that feed, 

 and by the rains that fall, upon the land — some remains in the deeper 

 roots, and some is again, year after year, employed in feeding the 

 new growth of grass — still a sufficient quantity is every season 

 brought up from beneath, gradually to enrich the surface with valua- 

 ble inorganic matter at the expense of the soil below. 



3^. Nor are mechanical agencies wanting to increase this natural 

 difference between the surface and the under soils. The loosening 

 and opening of the clay lands by the roots of the grasses allow the 

 rains more easy access. The rains gradually wash out the fine par- 

 ticles of clay that are mixed with the roots, and carry them down- 

 wards, as they sink towards the subsoil. Hence the brown mould, as 

 it forms, is slowly robbed of a portion of its alumina, and is rendered 

 more open,*Hvhile the under soil becomes even stilTer than before. 

 This sinking of the alumina is in a great measure arrested when the 

 soil becomes covered with so thick a sward of grass as to break the 

 force of the rain-drops or of the streams of water by which the land 

 is periodically visited. Hence the soil of some rich pastures contains 

 as much as 10 or 12, of others as Httle as 2 or 3 per cent, of alumina. 



4°. The winds also here lend their aid. From the naked arable 

 lands, when the weather is dry, every blast of wind carries off a portion 

 of the dust. This it suffers to fall again as it sweeps along the surface 

 of the grass fields — the thick sward arresting the particles and sifting 

 the air as it passes through them. Everywhere, even to remote dis- 

 tricts, and to great elevations, the winds bear a constant small burden 

 of earthy matter;* but there are few practical agriculturists who, du- 

 ring our high winds, have not occasionally seen the soil carried off in 

 large quantities from their naked fields. Upon the neighbouring grass 

 lands this soil falls as a natural top-dressing, by which the texture of 

 the surface is gradually changed and its chemical constitution altered. 



5^. Another important agency also must not be overlooked. In grass 

 lands insects, and especially earth-worms, abound. These almost 

 nightly ascend to the surfice, and throw out portions of finely-divided 

 earthy matter. On a close shaven lawn the quantity thus spread over 

 the surface in a single night often appears surprising. In the lapse of 

 years the accumulation of the soil from this cause must, on old pasture 

 fields, be very great. It has often attracted the attention of practical 

 men,t and so striking has it appeared to some, that they have been in- 



* It. lia=! been observed that on spots purposely sheltered from the wind and rain on every 

 Bide, th'? quantity of dust that is collected, when pressed dotrn, is in 3 years equal to one line, 

 or in 36 years to one inch in thickness. — Sprengel, Z^hre vom Diinger, p. 443. 



t The permanence cf a fine carpetmg of rich sweet grass upon a portion of his farm is 

 ascribed (by Mr. Purdie) to " the spevvings of worms, apparently immensely numerous, 

 which incessantly act as a rich top dressing."— Pr/ze Essays of the Highland Society, I. 



