Soil. 23 



3. Clay. A clay soil is distinguished above every other 

 for its tenacity. It is principally composed of particles of 

 earthy matter, many of them so small, that when separated 

 from each other, they are imperceptible to the touch, and 

 will easily float in water ; yet these minute particles form 

 a soil, that is far more tenacious and adhesive than any 

 other species of earth. Clay swells considerably when it is 

 wet. It then feels soft and clammy, and adheres roach to the 

 plough, or to any thing with which it comes in contact. In 

 that state, it will hold water like a dish. When dry, it con- 

 tracts in volume, and becomes as hard and tenacious as bricks 

 when prepared for the kiln. In a dry summer, the plough 

 turns it up in great clods, scarcely to be broken or separated 

 by the heaviest roller. It requires, therefore, much labour to 

 reduce it to a state fit for producing either corn or grass ( 77 ), 

 and it can only be cultivated, when in a particular state, and in 

 favourable weather. Though it will therefore, under a pro- 

 per system of management, yield great crops, yet being culti- 

 vated at a heavy expense, requiring stronger instruments, and 

 stouter horses, it is seldom that much profit is obtained, un- 

 less when occupied by an attentive and industrious farmer. 

 The value of clay, and of every other soil, depends much 

 on the quality of the substances on which k rests, for an 

 open subsoil renders it more tractableand productive ( 78 ). In- 

 deed, a subsoil of sand or gravel, under the clay, and near 

 to the surface, is of all others the most desirable. But such 

 a favourable formation of soil and subsoil is rarely to be met 

 with. Clay, resting on whin rock, being more mixed with 

 earthy substances, is always more friable, and more produc- 

 tive, than when it is incumbent on freestone, or coal me- 

 tals. But by far the greatest proportion of this species of soil 

 in Scotland, rests on a coarse species of clay, of a hard and 

 obdurate nature, mixed with ferruginous matters, and known 

 under the name of till. It is commonly of a considerable 

 depth, and so close and adhesive, that no water will sink 

 through it. 



In improving a clay soil, it is of much importance, to 

 ameliorate its texture, by a suitable mixture of common 

 sand, sea-sand, and above ail, of limestone gravel, where 

 that can be obtained. Peat-moss also, that has for some 

 time been dug up, and exposed to the action of the atmo- 

 sphere, may be used with advantage. It is likewise neces- 

 sary, in the course of its cultivation, to enrich it with putrid 

 and calcareous manures ; and it may be much improved by 

 having a considerable quantity of ashes mixed with its putre- 



