98 MOUNTAIN AND MOORLAND 



plant helps more than the Bog Moss. What is it 

 that happens ? The firmer dead parts of the plants, 

 bathed in stagnant, airless water, undergo a peculiar 

 change. It is not like ordinary rotting, which requires 

 the active intervention of bacteria. They change into 

 carbon compounds with little oxygen, and they may 

 finally become pure carbon. The membranes and 

 fibres of a carpet of vegetation become pressed 

 together and form peat, in a compact crust which 

 does not mix with the underlying mineral layers. 

 These, indeed, are eventually several feet below. It 

 may be said, then, that peat is made of the fibrous 

 parts of plants which have undergone very incom- 

 plete rotting; it is slightly aerated and rich in brown 

 ulmic acid and blacker humic acid; it is very spongy, 

 and does not let the water through as vegetable mould 

 does; it dries very perfectly on an exposed slope, but 

 it becomes heavily waterlogged when the evaporation 

 or seeping away of the water is slow. Peat seems 

 to be restricted to the colder parts of the globe, for 

 its formation implies slow and partial decomposition 

 in presence of abundant water. The browner it is 

 the less decomposition there has been, and the better 

 it will be for burning. While peat is mainly due to 

 Bog Mosses and other bog plants, it may be formed 

 to some extent when a forest has been cleared away 

 and when the ground becomes too dry for earth- 

 worms. The accumulation of vegetable matter may 

 continue for a time and form a peaty crust the forest 

 turns into a dry heath. Later on some subsidence or 

 blocking of drainage may turn the heath into a peat 

 bog. 

 Cutting the peat year after year does not neces- 



