CHAP. II.] EARTHS. 23 



Should the water, instead of being" afforded a 

 vent by drainage, be suffered to accumulate for 

 many years, till it completely liquefies the peat, 

 the soil becomes what is called a morass, or 

 quagmire ; and it can no longer be trodden on, 

 as it will engulf any substance resting upon it. 

 A still further accumulation of water will, in 

 the course of years, cause the bog to burst its 

 bounds, and overflow the surrounding country ; 

 as the Solway Moss did many years ago, and 

 as bogs in Ireland have done frequently. An 

 excess of vegetable matter on a sandy or gra- 

 velly subsoil differs from the common black 

 peat in being more decayed, as it retains less 

 water; and in being mixed with a portion of 

 the primitive earth, which, from its loose 

 texture, becomes easily detached from the sub- 

 soil, and mino'les with the surface soil, and in 

 this state the peaty matter forms what is called 

 heath mould. 



There are few things which appear more in- 

 credible to those who have not studied the 

 subject, than the great variety of earths which 

 enter into the composition of plants ; and yet 

 there can be no doubt of the fact, for when 

 different kinds of plants have been burnt, 

 and their ashes analysed, as many as eleven 

 different kinds of earths have been found in 

 the ashes. These earths vary in different plants, 

 but the most common kinds in garden vegeta- 

 bles are potash, soda, lime, sulphur, phos- 

 phorus, silica, magnesia, alumina, and a very 

 small quantity of iron. Some of these earths 

 are only found in plants in combination with 

 oxygen or chlorine, and the same earths are 



