52 THE PRINCIPLES OF 



In the third place, we occasionally find a clay soil or a stiff 

 loam resting upon an exceedingly tenacious blue clay. Such 

 soils are " holding " in their nature. They will hold fertilizing 

 matter and moisture with great tenacity, and they may be 

 converted into useful fertile soils by the aid of artificial 

 drainage. But in their natural condition such soils are apt 

 to become waterlogged, and consequently unprofitable for 

 arable purposes, although they form a very excellent basis 

 for permanent pasturage. 



Sometimes a clay soil or a stiff loam rests upon sand or 

 gravel, giving highly favourable conditions. And, in the fifth 

 place, we find the reverse, namely, a light sand resting upon 

 a clay. That is a favourable condition, not only because the 

 clay assists the sand to hold moisture, but because the marl 

 or clay from below may be dug up and spread upon the 

 surface, a system extensively carried out in the county of 

 Norfolk, and which is also applied to the fen-lands of Lincoln- 

 shire, where the clay has been the means of reclaiming or 

 rendering useful thousands of acres of land. 



Sixthly, we find soils in which the rock is so near the 

 surface that the plough-sole may be heard rumbling on the 

 top of the rock. Sometimes the plough is arrested by the 

 rock itself, and the horses are stopped. Now, when the 

 surface soil is thin and rests upon the rock, we have a 

 good example of what was stated in a previous chapter, that 

 is, a soil which may give a good analysis, but is deficient 

 in quantity. Of course a great deal depends upon the nature 

 of the rock. A rock of a moist character, conserving moisture, 

 and of a fissured nature, is not unfavourable. It is stated 

 with reference to hops, for example, which are a deeply-rooted 

 plant, that they prefer a soil of this description with a fissured 

 and rocky sub-soil, or rubbly sub-soil, into which the roots 

 may penetrate to a great depth. 



In other cases the rock is of an arid character, in which 



