302 THE EEGOLITH 



material in situ, though differing radically in both composition 

 and origin from those just described, are those portions of the 

 regolith which result from the gradual accumulation of organic 

 matter with only small amounts of foreign detritus; which are 

 made up almost wholly of the combined accumulations, organic 

 and inorganic, of growing plants. Such may be found in all 

 stages of formation, in enclosed ponds or lakes, without appre- 

 ciable inlet or outlet, being merely due to standing water in 

 low places. ' * Such pools, when not exposed to periodical drying 

 up, are invaded by a peculiar vegetation, first mostly composed of 

 conferva, simple thread-like plants of various color and of prodi- 

 gious activity of growth, mixed with a mass of infusoria, animal- 

 cules, and microscopic plants, which, partly decomposed, partly 

 containing the floating vegetation, soon fill the basins and cover the 

 bottom with a coating of clay-like mould. So rapid is the work 

 of these minute beings, that in some cases from 6 to 10 inches 

 of this mud is deposited in one year. Some artificial basins in 

 the large ornamental parks of Europe have to be cleaned of such 

 muddy deposits of floating plants, mixed with small shells, every 

 three or four years. 



'*When left undisturbed, this mud becomes gradually thick 

 and solid ; in some cases, of great thickness ; affording a kind of 

 soil for marsh plants, which root at the bottom of the basins or 

 swamps and send off their stems and leaves to the surface of 

 the water or above it, where their substance becomes in the 

 sunshine hard and woody. 



'*As these plants periodically decay, their remains of course 

 drop to the bottom of the water; and each year the process is 

 repeated, with a more or less marked variation in the species 

 of the plants. After a time the basins become filled by these 



Fig. 30. — Section across a small lake, a, bed rock; td, drift; cc, growing 

 peat; dd, decaying peat; ee^ climbing bog. 



successive accumulations of years or even centuries, and the 

 top surface of the decayed matter, being exposed to atmospheric 

 action, is transformed into humus and is gradually covered by 



