34 



AGRICULTURE. 



clay have come from these old rocks, sand from one kind of 

 rock, white clay from another kind of rock, blue clay from 

 another. The nature of the soil will therefore depend largely 



upon the nature of 

 the rock from which 

 it came. This sand 

 or clay may have 

 come from the break- 

 ing up of the rocks 

 that are to be found 

 just under the soil ; in 

 that case the soil is 

 likely to be shal- 

 low. But usually it 



Fig. 18 Soil formed from rock underneath, a soil has COme from 

 with grass growing in it ; b subsoil, coarser and 

 more rocky ; c coarse, loose rock; d rock in layers, at 3. distance, a lonf 

 cracked, d changes to c, c changes to b, and b to a. 



distance it may be, 



and has been carried to its present place by water and ice, and 

 spread out over the old rocks. In this latter case the soil may 

 be very deep and mixed. We can now explain why the ; soil 

 ^n some places is quite different in its nature from the rocks 

 under it, and why there is such a variety in the same locality 

 and on the same farm. One field may be clayey, and across 

 a stream we may find a sandy soil they have come from 

 different places, and have been washed down by the waters 

 and spread out at quite different times. 



A step farther back can now be taken. We go to the hills 

 - to the great piles of rock. We observe that the old rock is 

 weathered. If we break off a piece, the fresh surface shows a 

 different appearance from the old weathered surface ; it is 

 generally harder. We can rub off some of the old weathered 

 surface ; what we rub off is the weathered rock fine sand or 

 fine clay. We observe long cracks or crevices, some narrow 

 and fine ; some wide and deep. The rains find their way into 



