THE TEMPORARY MISSISSIPPI RIVER 425 



rise from 25 to 40 feet above the flood-plain of Cedar River. 

 Although the slope is not apparent to the eye, the terraces have a 

 gentle inclination to the south. The surface of these terraces is 

 approximately 660 feet above sea level at their northern extremity 

 at West Liberty and Moscow, and from these points they slope 

 gently to their southern extremities in Louisa County, 18 miles 

 distant, where they have an elevation of 615 feet. Scattered over 

 the entire area, but especially in the vicinity of Cedar River, 

 there are low-lying sand mounds or dunes. On the west side 

 of Cedar River, the terrace is remarkable for its uniform width, 

 since out of the 22^ miles of its total length, it maintains for 

 a distance of 14 miles an average width of 4! miles. Here also, 

 the terrace is continuous for its entire length, but, on the east side 

 of the river, it is broken into nine remnants. Immediately west 

 of Moscow, on the west bank of Cedar River, is an island-like high- 

 land which is a half mile distant from the main upland to the north- 

 west, the surface of which rises, on the average, 75 feet above the 

 level top of the surrounding terrace. This upland remnant has 

 an area of about i^ square miles. The bluff line on the north and 

 east is cut into the Devonian limestone and is therefore very well 

 defined. Toward the south, and especially toward the southwest, 

 the border of the remnant is less conspicuous, due to the presence 

 of numerous sand dunes. 



Exposures of the materials in the terraces are not numerous, 

 because of the extreme youthfulness of the topography and the 

 slight relief of the region. The surface materials consist of fine 

 yellowish to brownish or drab-colored loess-like silt and sands, the 

 latter forming the dune areas previously described. A few scattered 

 bowlders dot the terrace surface. Most of the wells on the terrace 

 are about 30 feet deep, but one at Nichols is recorded to have pene- 

 trated at least 250 feet^ of unconsolidated material. The various 

 outcrops, for the most part, show a fine- to medium-grained white 

 to light-brownish sand, the strata of which in the northern part 

 of the terrace are thin and essentially horizontal. Farther south, 

 the sand shows cross-bedding and numerous thin layers of pebbles, 

 the largest of which have a diameter of less than i inch. 



'J. A. Udden, "Geology of Muscatine County," op. cit., Vol. IX (1899), p. 355. 



