38 SOILS AND MANURES 



accumulated in enormous quantities in certain places. 

 Local deposits often extend over an area of several square 

 miles, and may be as much as 50 feet thick. It is calcu- 

 lated that in Ireland alone over 4,000 square miles are 

 covered with peat. Peat bogs are formed by the growth of 

 mosses, sphagnum, and other aquatic plants. New genera- 

 tions grow and flourish on the surface, and are nourished 



FIG. 3. Section of Peat Bog. 



by the products of partial decomposition of previous 

 generations below. The moss accumulates relatively fast 

 in some cases. Growths at the rate of about two and a half 

 inches annually have been recorded. Examination of a 

 section of a bog from which peat has been cut reveals in- 

 dications of continuous change from above downwards. 

 The topmost layer is usually of a light golden or fawn 

 colour ; this merges gradually into dark brown, and 

 finally into black at a depth of two or three feet. The 

 texture of the material corresponds to the gradations of 

 colour ; the upper layers are more fibrous and spongy, the 

 lower are harder and more compact. These layers also 



