52 



THE I K K I G A T I N AGE. 



ihe individual particles lie so close together that water 

 poured upon the surface of a clay often remains there a 

 long time, soaking into the clay with extreme slowness. 



Silt is somewhat coarser than clay; the various grades 

 of sand being still coarser; and the gravels including the 

 largest particles which are recognized as belonging to a 

 true soil. The various grades of rock fragments recog- 

 nized in the soil vary then from particles of about one- 

 tenth of an inch in diameter to those so small as to be 

 separately invisible to the naked eye. 



Soils are classified in two ways, namely, as to the 

 method of their formation, and as to their composition. 

 According to the first classification, are recognized (1) 

 Sedentary soils (soils in place), and (2) Transported soils. 



Sedentary soils are those which have been formed 

 just where they are found and are subdivided into a (a) 

 Residuary, and (b) Cumulose soils. 



Residuary soils have been made from the decay of 

 the rocks on which they lie and partake more or less of 

 the composition of the underlying rocks. They have usu- 

 ally lost considerable of their soluble constituents, these 

 having been washed away by rains. These soils are not 

 generally very deep, the underlying rock being compara- 

 tively ,close to the surface. Residuary soils may be fer- 

 tile or not, depending on the kind of rock from which 

 thev were formed. 



Running Water Cuts Deep Valleys in the Surface of the Earth and Carries Away 

 the Debris to Form Soil at Some Other Place. 



Cumulose soils are those formed in swamps and 

 marshes. They consist largely of organic matter which 

 has come from the partial decay of the marsh plants. 

 They contain also the earth which has been washed down 

 from the surrounding higher lands. Muck and peat are 

 examples of the cumulose soils. 



The principal classes of transported soils are (1) 

 Alluvial, (2) Aeolian, and (3) Drift soils. 



Alluvial soils are those which have been carried by 

 water and deposited at some distance from their original 

 source. They commonly show more or less distinct layers 

 as the coarser particles are naturally the first to settle 

 out, the finest particles being the last to be deposited. 

 The materials found in these soils vary widely in depth, 

 being usually shallow on high lands and deep near the 

 mouths of the large rivers. The soils in the river valleys 

 are alluvial and have been carried down by the stream 

 during the flood season and deposited as the speed of 

 the current decreased. Alluvial soils are usually fertile, 

 but it will be seen that the character of these soils wil! 

 vary with the character of the rock material of the up- 

 lands from which they are derived. 



Aeolian soils are those which are composed of par- 

 ticles transported by the wind and are therefore some- 

 times called wind formed soils. These soils are also 

 called "loess" and it is supposed that considerable areas 



Nodules on Soy Bean Roots. 



of soils in central United States are wind formed. They 

 vary in thickness from a few feet to over one hundred 

 feet and are soils of considerable agricultural value. 



Drift soils are those which have been transported by 

 glaciers. A large part of northern United 

 States is covered by drift soil which was car- 

 ried down from the north by the great glaciers 

 which at one time covered this region. Drift 

 soils are characterized by the presence of 

 boulders and rounded pebbles. They are quite 

 variable in character and many different kinds 

 of soil may be found in a single farm located 

 in the glaciated region. Drift soils are usually 

 productive. 



Soils are classified according to composition 

 into clay, sand, loams, peat (or muck) and 

 limestone soils. 



A clay soil is one that contains over 60 per 

 cent of clay particles. It is the hardest soil to 

 work as it is sticky when wet and when dry 

 becomes so hard that it can hardly be pulver- 

 ized. In very dry weather crevices and cracks 

 open in clay soils, letting in air and allowing 

 the evaporation of water, which dries and in- 

 jures the roots, sometimes breaking them. A 

 clay soil unless well drained is likely to be 

 cold and unresponsive. These soils are usually 

 high in "potential'' plant food, especially pot- 

 ash, but need to be carefully handled to enable 

 the plant to make use of this food material. 

 They are usually retentive of added plant food 

 and are, therefore, soils which can be liberally 

 fertilized without fear of great loss of the ap- 

 plied material. 



Sandy soils are those containing a very large propor- 

 tion of sands (75 per cent or more). They are just the 

 opposite of clay soils, being too open and porous, while 

 the clays are too compact and impervious. The^y hold 

 but little water and crops growing on them are likely to 

 suffer in hot, dry weather. These soils are usually low 

 in fertility and have little power to retain added plant foot 

 as the excess of sotuble material in manures and fertilizers 

 used on them is likely to leach through them with the 

 water. But no soil is so poor that it cannot be made to 

 grow a crop, so even these sandy soils can be made pro- 

 ductive by the liberal use of organic matter, and the addi- 

 tion, if necessary, of lime, phosphoric acid and potash. 

 They are warm soils, work easily, and if properly handled 

 are often profitably used for early truck crops especially. 

 Peat or muck soils contain very large amounts of 

 organic matter, some of them having as much as 80 per 

 cent of this. They are found in the beds of former lakes 

 or swamps, and are formed by the partial decay and modi- 

 fication of vegetable matter under water, and usually con- 

 tain but little earth. Peat is an intermediate product be- 

 tween vegetable matter and coal and perhaps in course of 

 time would be converted into coal. The name muck is 

 sometimes applied to a soil in which the organic matter is 

 in a more advanced state of decay than in true peat. 



