TERRACES OF THE MARL-LOESS 163 



These terraces are exceptionally well developed in the Mumford hills 

 and at a number of points in the reojion to the east, southeast, and south 

 of New Harmony. Figure 1 of plate 15 shows the appearance of the 

 Mumford Hill terrace as seen from the south. The easterly slope is 

 readily detected. The core of the hills is of rock, which at a few points 

 rises as marl-free " islands '' above the general plain of the marl-loess, 

 the remainder being buried, as brought out by the water wells, beneath 

 the mask of marl-loess. Southeast of New Harmony the buried topog- 

 raphy is often quite rugged, although, as shown in figure 1, plate 15, 

 which is a reproduction of a view taken in the south half of section 5, 

 township 5 south, range 13 west, about 3 miles southeast of New Har- 

 mony, the surface is frequently as flat as a floor. In such regions the 

 variations from the plain are either brought about by the projection of 

 rock "islands" through the marl-loess or by the action of the streams 

 in cutting sharp V-shaped ravines. All the minor drainage has, in fact, 

 been developed since the deposition of the marl-loess, there being few 

 original depressions of importance except those due to thinning along 

 the eastern margin of the deposit. The common range in altitude of the 

 terraces is from 440 feet to 500 feet above tide, very fine examples being 

 noted at the latter altitude in the Mumford hills and south of New Har- 

 mony (figure 2, plate 15). The tenaces in both cases subside to the 

 eastward to altitudes of 460 or 440 feet, at which levels there are exten- 

 sive deposits at intervals throughout the area on both sides of the Wabash 

 as far north as Hazelton. 



Discussion of Evidence 



The maximum development of the marl-loess, occurring as it does 

 along the valleys of the Wabash and White rivers, and its limitation to 

 belts of moderate width on each side of the valleys, appears to indicate 

 that the two rivers were intimately connected with the furnishing of the 

 materials for the deposits. 



The range of the marl-loess, as indicated by its typical yellowish color 

 its stratification, its fossils, and by its terraces, points to a controlling 

 factor which worked within certain fixed limits in the region under dis- 

 cussion, this being a horizontal line or level at an altitude of 500 feet 

 above tide, or approximately 120 feet above the present flood plain of 

 the Wabash. 



The fact that, notwithstanding the essentially contemporaneous origin 

 of the common and marl-loess deposits, the former are weathered and 

 leached throughout, while the latter are frequently practically unoxi- 

 dized and unleached at a depth of 2 or 3 feet, would appear to indicate 

 (1) that the common type is richer in its iron constituent, (2) that the 



