FIG. 11-3 (a) profile of a podiol 

 (mor) from sandy glacial till 

 under coniferous forest In Maine 

 (courtesy Charles E. Kellogg) 

 (b) profile of a gray-brown 

 podiolic soil (mull) formed 

 from loess under oak-hickory in 

 Iowa, (c) profile of a chernoiern 

 formed from glacial drift under 

 prairie in South Dakota— white 

 spots are calcium carbonate, 

 (d) profile of a sieroiem, a desertic 

 soil, derived from alluvium under 

 sagebrush in Nevada, (e) profile 

 of a latosol derived from gneiss 

 under broad-leaved evergreen 

 forest in Brazil. Pinholes and 

 larger channels, formed by roots 

 and insects, extend to 6 feet. 

 Scale in feet and inches 

 (courtesy Roy W. Simonson). The 

 lettering along the margins of 

 the profiles indicate the soil horizon: 

 (see page 170). 



An excess of some elements is harmful. Too 

 much fluorine in drinking water causes motthng of 

 teeth and possibly pathological changes. Selenium in 

 soils of arid plains becomes dangerous when it 

 reaches 0.5 ppm, since some grasses, asters, and cer- 

 tain legumes absorb and retain it in concentrations 

 that can be highly injurious to herbivorous animals. 

 Wild animals have apparently learned to avoid eating 

 these particular plants, but domestic stock blunder 

 into them, eat them, and die (Knight 1937). Certain 

 plants concentrate specific elements, a factor which 

 may afifect the food habits of animals. Black tupelo 

 concentrates cobalt, and inkberry concentrates zinc to 

 a much greater extent than do other species growing 

 in the same areas (Beeson et al. 1955). 



Climate 



Water, temperature, and wind are important 

 weather factors affecting soil formation. Water is an 

 agent of rock erosion and transportation, sorting, 

 and deposition of soil-building erosion products. 

 Water freezes and expands in cracks and crevices 

 of massive rock structures, breaking them into frag- 

 ments and particles. Daily and seasonal heating and 

 cooling cycles produce cracking because of different 

 coefificients of expansion of the minerals in the rock. 

 Wind erosion is particularly devastating in arid re- 

 gions ; fine soil particles may be lifted and transported 

 many miles. 



Weathering of rock is a chemical as well as physi- 



68 Ecological processes and dynamics 



