NATURAL ORDER OF ROCKS. 137 



exhibiting the undulating character of the plain, and also the more 

 elevated part at 5, may rest upon similar or dissimilar rocks, according 

 to the order of superposition. At 2, 3 and 4, the soil will be different 

 for a short space, and at 6 the perpendicular rock rises to the surface. 

 Thus the undulating character of the land brings to the surface dif- 

 ferent kinds of rocks which produce corresponding differences of soil. 

 Generally these valleys have been produced by water, which has 

 washed away parts of parallel layers of horizontal rock. A more 

 diversified soil may be seen in the next cut, where three different in- 

 clinations of rock are perceived, at 1, 2 and 3. 

 l 



On the plain from a to b a change in the soil would appear, and also 

 at c ; though, from the extent of the plain no special elevations may 

 be noticed. But on rising the hill at d, the soil would present a dif- 

 ferent character, until arriving at 2, where the edges of the rocks 

 would present other changes in the soil, and these may vary with every 

 inclined layer there noticed. Again, at 1, the perpendicular layers 

 are much thinner, and the soil, consequently, may there vary with 

 every bed in the group, or the whole may be mixed. 



The natural order in the position of stratified rocks is also to be 

 considered. Thus at a 6 and c, in the first cut, there may be sand- 

 stone, lime-stone, or slate, and wherever these or any one of them are 

 found, they will always have the same relation to the rocks above and 

 below. So that knowing this relative position and finding a particular 

 bed on the surface, you will know what rocks are below it and the 

 order of their superposition. No where, for example, will the rocks 

 a or c be found above the rock d. Thus the relative age of each 

 rock is determined, the lowest being always the oldest ; and thus also 

 in digging or sinking a shaft you will know from the uppermost rock 

 what rocks, in their order, you will meet with. This is useful to the 

 agriculturist who would improve his soil, by bringing upon it a certain 

 kind of rock or soil, as clay, marl, or lime, of which it may be desti- 

 tute, as he might go to a valley, not far distant, to obtain it, instead of 

 digging to the bed on his own land. It will be found, likewise, that 

 if the soil is not good on a certain rock, it may be much improved 

 where two different rocks meet, as in the valleys denoted in the cuts ; 

 for one may be a cold clay and the other a dry sandy soil, but these, 

 on mixing, mutually modify the properties of each other. Such will 

 be good soils for the growth of turnips, while the addition of a stratum 

 of lime would make it good for wheat. 

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