28 FORMATIONS AT PRESTON.—LOESS. 
Dr. Shumard found on the Red river, twenty-six miles from Fort Washita, a deposit of 
ash-colored loam, twenty-five feet thick, containing terrestrial and fluviatile shells of the genera 
Lymnea Physa, Planorbis, Pupa, and Helix; the whole resembling species found in the loam at 
New Harmony, Indiana, and elsewhere in the Mississippi valley.! This formation along the 
Mississippi constitutes what are known as the ‘‘ Bluffs," and is a fluviatile accumulation laid 
down by the river when the region was at a lower level. In other words, it is an ancient allu- 
vion. Its thickness and known extent along the Mississippi render it very probable that it 
will be found along most of the principal tributaries of that river. A similar deposit is found 
along the valley of the Rhine, Its thickness is from 200 to 300 feet, and it is a yellowish-grey 
loam, consisting chiefly of clay, combined with sand and carbonate of lime. The same deposit 
is found along most of the principal valleys or tributaries of the Rhine; it evidently having been 
contemporaneously deposited. It is known in Germany under the name of loess. 
he occurrence of a formation along the Red river similar to those described, leads me to 
believe that it will be found along most of the rivers which are tributary to the Mississippi, and 
it is quite probable that, in the environs of Preston, and even over broad tracts of that region, 
there are extensive superficial alluvial deposits, which afford a soil thata oan scarcely be sur- 
passed for its richness and fertility, 
l Report of Captain Marcy—Appendix D, p. 183, 
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