4<3 FARM DEVELOPMENT 



sorted till." Where water flowing from the melting ice 

 washed the loose materials about and deposited them in 

 layers of clay, silt, sand, gravel, etc., the geologists call it 

 " assorted till." Some of the best soils are those where 

 the glacial till is unassorted. The farmers of the middle 

 northwest have the great glacier to thank for mixing to- 

 gether clay, sand and particles of all kinds of rocks, thus 

 making soils wonderfully adapted to the growth of useful 

 plants. These soils of mixed materials furnish ideal 

 mechanical conditions for the roots of plants, contain 

 the needed variety of mineral plant food, conserve the 

 remains of plant or animal life as organic fertilizers, 

 favor the elaboration and storage of plant food as well as 

 the absorption and conservation of soil moisture, serve 

 as hospitable homes to useful soil bacteria, and are easily 

 handled with cultivating implements. 



Assorted till formed poor soils. Wherever the water 

 assorted the great body of materials drifted along by the 

 glacier, some poor soils are found. Layers of sand left 

 at the surface give us sandy soils, likewise layers of 

 gravel or of boulders make very poor soil, and even 

 layers of dense clay without a mixture of sand are less 

 valuable than soils made up of these materials mixed. 

 Sandy soils in the regions of ample rainfall have, in many 

 instances, been so covered with vegetation and so filled 

 with decaying organic substances, that they retain water 

 very well and nourish large crops. Even gravelly soils, 

 where moisture is abundant, are gradually so changed 

 that they raise crops of native plants and make fair 

 agricultural soils. Clay soils which are too dense to 

 make very good water reservoirs, or to allow the en- 

 trance of air, are, likewise, sometimes made into very 

 productive soils by the plants which grow on them. 

 These clay soils, in some cases, cover large areas. In the 

 valley of the Red River of the North is an example. The 

 glacial ice melting in "Ancient Lake Agassiz " (see 



