Ch. 6] THE LITTORAL ENVIRONMENT 121 



depends on the type of material supplied to the stream, the climatic and 

 topographic conditions at the source, and the extent of transportation. 

 Channel deposits usually have a higher proportion of coarse material 

 and therefore constitute better aquifers. The deposits are usually thin, 

 and always lenticular in cross section. If a stream is actively aggrad- 

 ing, aquifers of considerable extent may be formed. There are ex- 

 tensive sand beds, primarily of glacial-outwash origin, in the valley 

 of the Ohio River in the vicinity of Louisville, Kentucky, where large 

 supplies of water are pumped daily (Rorabaugh, 1948). Much water 

 is pumped from valley-flat deposits of the Platte River in Nebraska, 

 Wyoming, and Colorado. 



The very extensive Tertiary deposits of western Nebraska, North and 

 South Dakota, eastern Montana and Wyoming, and western Kansas 

 are good examples of valley-flat sediments. They contain much per- 

 meable material, particularly that close to the mountain fronts, and 

 they form good aquifers in many places. At some distance from the 

 mountain sources of material, much clay is interbedded with sand and, 

 though the sands yield some water, the permeability is usually rather 

 low. 



CONTINENTAL ENVIRONMENTS— SWAMP 



The Swamp Environment 



Swamp sediments are usually poor aquifers, for the materials are 

 generally fine-grained. Peat and coal beds may be permeable. Lig- 

 nite beds in western North and South Dakota and eastern Montana 

 provide water to many wells. The water is usually colored brown and 

 in many places is rather highly mineralized. Coal beds provide water 

 for many wells and springs in Pennsylvania. 



MIXED CONTINENTAL AND MARINE ENVIRONMENTS 



The Littoral Environment 



Sediments of the littoral zone have a wide range in composition — 

 from shale or limestone to boulder deposits. It is usually unnecessary 

 to distinguish aquifers of littoral origin from marine sediments as 

 sources of ground water, because they are of limited extent, particu- 

 larly at right angles to the shore line. In some places, however, recog- 

 nition of their origin may be significant in their evaluation as water- 

 bearing beds. 



