642 THE PLEISTOCENE PERIOD 



coast of Maine, where marine shells occur up to elevations of 200 

 feet or more, 1 and to still greater heights farther north. 



Loess 



The term loess is used both as a textural and a formational name. 

 Lithologically, it is a silt intermediate between sand and clay. It 

 is generally free from stones of all sorts except concretions developed 

 in it since its deposition. In the exceptional cases where stones 

 occur in it, they are confined in most cases to its very bottom, or to 

 loess which has slumped or been washed down from its original posi- 

 tion. It is interstratified with sand in some places. 



Composition. The loess contains many angular, undecomposed 

 particles of the commoner carbonates (calcite and dolomite) and 

 silicates (feldspars, amphiboles, pyroxenes, micas, etc.), and a few 

 of the rarer silicates. Magnetite also is a common, though never an 

 abundant, constituent. All these are subordinate to quartz. These 

 constituents strongly suggest that the material of the loess was 

 derived from the rock-flour of the drift. In color it is generally 

 buffish, but in not a few places it has a grayish (bluish) cast a few 

 feet below the surface. 



Loess stands readily with vertical faces (Fig. 533) for long 

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

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

 silt of the road-bed is washed or blown away, while that on either 

 side stands up with steep or even vertical slopes. Many weathered 

 faces of the loess show a rude columnar structure (Fig. 533), the 

 columns being one to several feet in diameter. The loess, as a rule, 

 shows no stratification, but in its coarser phases there is some sug- 

 gestion of such structure, and where interbedded with sand, strati- 

 fication may be distinct. 



Distribution. The best known loess in America and Europe is 

 associated with glacial drift, though loess extends far beyond the 

 borders of the drift in some directions, in both continents. In 

 China and other lands of Asia, where loess has great development, it 

 is not generally associated with glacial formations. 



In North America the loess does not occur east of the Mississippi 

 basin, and has little development east of the Wabash River. It 

 is widespread in Illinois and the states along the Missouri, and in 



1 Stone, Jour. Geol., Vol. I, pp. 246-254, and Bastin, Rockland, Me., folio, 

 U. S. Geol. Surv. 



