56 SOILS : PBOPEBTmS AND MANAGEMENT 



the oscillation of the ice front. With the ice melting 

 rapidly on the hilltops, these lakes were constantly fed 

 by torrentb from above which were laden with sediment 

 derived not only from under the ice, but also from the 

 unconsolidated till sheet over which it flowed. As a 

 consequence, there w^ere in the glacial lakes deposits rang- 

 ing from coarse delta materials near the shore to fine silts 

 and clay in the deeper and stiller water. Such materials 

 now cover large areas (see Fig. 4), not only in New York 

 State and along the Great Lakes, but also in the Red 

 River Valley and in the northerly inclined valleys of the 

 Rockv Mountains and the Cascade and Sierra Nevadas. 

 They make up by far the most important lacustrine 

 soils. 



43. Lacustrine soils — glacial lake. — Glacial lake soils 

 probably present as wide a variation in physical char- 

 acteristics as any of our great soil provinces. Being 

 deposited by water, they have been subject to much 

 sorting and stratification, and range from coarse gravels 

 on the one hand to fine clays on the other. They are 

 generally found as the lowland soils in any region, al- 

 though they may occur w^ell up on the hillsides if the 

 shores of the old lakes encroached thus far. The color 

 of such soils varies from gray to black, according to 

 the degree of organic matter present. The humus con- 

 tent of such soils, as with the glacial till, varies with 

 climate^ and may be high, low, or medium according 

 to conditions. The thickness of glacial lake deposits is 

 variable, ranging from a few feet to many feet. In 

 chemical composition they closely approximate the soil 

 from which they are derived. This is particularly true 

 as regards the presence of lime. The Dunkirk soil 

 of southern New York, a wash from the lime-poor 



