WITH AGRICULTURE AND PLANTING. 45? 



tion. In many parts of Sweden, as in Westrogothia, in 

 Scotland, &c., there occur many elevated regions, in 

 which gneiss and granite predominating, exclude to a 

 great extent all kinds of vegetation excepting lichens. 

 In the same districts we sometimes meet with pastures 

 and corn-fields interrupted here and there by bare rocks 

 rising but little above the surface, by which the value of 

 the ground is much diminished, and great impediments 

 opposed to its cultivation. 



As bare rocks are incapable of all cultivation, their dis- 

 tance from the under surface of vegetable mould must 

 also be of great importance. In the plains of the north of 

 Germany, for example, this distance is often so great 

 that a rocky surface is never found, while, on the contra- 

 ry, in other countries, especially such as are mountainous, 

 the roots of plants not unfrequently touch the subjacent 

 rock ; the variation between these extremes being of all 

 degrees. The effect of the distance of the surface of the 

 solid rock from the under surface of productive soil may 

 be both direct and indirect, and may vary much, not 

 only with reference to the species of rock, but also to 

 the vegetables. 



The surface of the solid strata of the earth has a di- 

 rect influence upon the cultivation of plants, because it 

 terminates the extension of their roots, and limits the 

 volume of the soil necessary for their sustenance. As the 

 length and direction of the roots vary exceedingly in dif- 

 ferent species, the difference of effect with regard to their 

 growth, and the approximation of the rock to the under 

 surface of the soil, must in general be so much the less 

 prejudicial in proportion as the roots decline from the 

 perpendicular; whence it follows, that certain grasses, and 



