ON THE COMPOSITION OF SOILS, &C. 193 



attraction, repulsion, &c. the accumulation, or 

 concentration, of the separate primitive sub- 

 stances ; or of vegetable and animal matter or 

 mould ; may be too great to raise and sustain 

 plants in a healthy and fruitful state, and such 

 may be the case with other bodies, either simple 

 or combined ; we therefore find that nature has 

 provided the means of averting those extremes, 

 by reducing and blending, or mixing them, and 

 this by the operation of insects and reptiles ; 

 as has been before observed, the earth worms 

 seem peculiarly formed for this purpose ; by their 

 means the different substrata of clay, calx, sand, 

 &c. are covered with a stratum, compounded 

 of the finely divided matter of its composition, 

 forming what is called loam, or the soil ; these 

 little creatures, in making their passages or in- 

 roads, have no other means of clearing their 

 way, than by eating the opposing matter, carry- 

 ing it to the surface and there throwing it up: 

 hence we find, that every part of the globe that 

 supports vegetables is furnished, or covered, 

 with an admixture of the different earths, form- 

 ing the soil, of greater or less depth j and the 

 depth of this stratum or covering, the degree 

 of concentration, and proportion of the different 

 substances, the nature of the substrata, as it 

 regards the percolation and retention of water j 



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