Formation of Soil. 



61 



FIG. 19. Relief Map of Wisconsin, showing the difference in topography be- 

 tween glaciated and non-glaciated surfaces. 



74. Formation of Humus Soils. There is a class of soils 

 having their origin in various types of swamps or marshes 

 which contain an unusual amount of organic matter in va- 

 rious stages of decomposition and which have by some 

 writers been given the name of humus or swamp soils, the 

 former name referring to the large amount of humus these 

 soils contain and the latter to the physical conditions under 

 which they have been formed. 



In many places in the higher latitudes and at consider- 

 able elevations nearer the equator where the surface is too 

 flat for ready drainage, and where the winter snows re- 

 main so long upon the ground that the summer is too short 



