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GEOLOGY 



Composition. 1 The loess contains angular, undecomposed 

 particles of the commoner carbonates (calcite and dolomite) and 

 silicates (feldspars, amphiboles, pyroxenes, micas, etc.), and several 

 of the rarer silicates have been identified. Magnetite also is a com- 

 mon, though never an abundant, constituent. All these are sub- 

 ordinate to quartz. These constituents strongly suggest that the 



Fig. 591. A section of loess in Iowa, showing its ability to stand with ver- 

 tical or even overhanging faces. (Calvin.) 



material of the loess was derived from the flour of the 

 mill. In color it is predominantly bufnsh brown, but in not a 

 few places it has a grayish (bluish) cast a few feet below the 

 surface. 



The loess often stands with vertical faces (Fig. 591) for long 

 periods, where sand or clay would be degraded into slopes. 1 

 on the loess tend to assume the form of little canyons, because the 



1 Sixth Ann. Kept. U. S. Geol. Surv., p. I'M. 



