THE SOIL AND SOIL FORMATION 57 



formation is on the surface of the water, on ponds and 

 lakes, where peat is formed by the growth of moss and 

 higher plants resting on the water. Many places are 

 to be found where peat a few inches to many feet in 

 thickness covers, or partially covers, areas of very 

 moist land, and even of lakes. In some cases, even 

 where the peaty substances are thick, sand and clay have 

 been washed in from adjacent hillsides, and have been 

 arranged in layers with the peat, or have been in- 

 timately mixed with it, and thus a soil of mixed vegetable 

 and mineral matter is formed. 



Soil formation under favorable conditions. Soil 

 formation on clay takes place more rapidly than on the 

 kinds of land above mentioned. Here the consistency 

 or texture of the land allows the entrance of both air 

 and water to the roots of the plants, and provides favor- 

 able conditions for the germination of seeds of the 

 higher forms of plant life. Here, too, lichens and mosses 

 were doubtless useful. In this soil their pioneer work 

 in preparing it for the higher flowering plants naturally 

 would be more rapid, or possibly in many cases un- 

 necessary. The higher plants in turn would send 

 their roots into the soil, opening up the clay and letting 

 in more air and water, thus helping to draw off the 

 excess of moisture, producing that mixture of air, water 

 and soil particles best adapted to the plants which we 

 grow in arable lands. 



The glacial mixtures of sand and clay, the alluvial soils 

 formed by running water, also the soils of mixed sand 

 and clay formed in situ from decaying rocks, were 

 even more easily formed into rich soils. Here the 

 lichens and mosses and the other small plants following 

 them could easily get hold and find at once conditions 

 of moisture, aeration and mineral plant food suited to 

 their growth. The larger giants here find many con- 

 ditions favorable to their growth, and the elaboration of 



