Intercollegiate Geological Excursion 873 



Stops for observation and discussion were made at strategic points every 

 few miles. From the first point, elevation 590 feet, the subaerial valley forms 

 below the Prospect terrace were noted. Here, as is generally true in any one 

 aIcw, nothing more than one older, outer, and higher, one younger, inner, and 

 lower valley slope is demonstrable; yet a broader study of the region suggests 

 that the valleys had been eroded here with respect to older base-levels of about 

 t)20 and 520 feet, and several younger and lower base-levels. It emphasized the 

 iiocd in physiographic study of an analytical investigation of a region from the 

 map as a necessary accompaniment of local field observation. 



The next stop was at an elevation of 900 feet on the top of a remnant of 

 the Prospect terrace. Here again, as in most cases, nothing conclusive is shown 

 by observation at one point in regard to the mode of origin of the Prospect 

 terrace or its relation to the higher levels. A broader study suggests, however, 

 that it was made by a marine planation of moderate amount resulting from a 

 submergence following a long period of subaerial erosion. 



The three higher terraces, on the other hand, as shown on the route through 

 Morris, Litchfield, and West Goshen, show very definitely plains cut nearly 

 liorizontally, but at successively higher levels. From the viewpoint of each lower 

 plain, the front of the next higher terrace is seen to trend as a dissected and 

 sloping wall across the landscape. The surface of each higher terrace has 

 •suffered also to a greater extent than those lower from subsequent subaerial 

 ■denudation. 



The consequences following from this interpretation of the Piedmont plateau 

 are most important, as it changes the conception of its mode of origin and of the 

 Tertiary history of the Atlantic slopes. It gives a suggestion of the geological 

 rapidity of completion of an erosion cycle in a region near the sea and of a 

 sequence of diastrophic rhythms there recorded. A similar control of the 

 topography of the seaward slopes should be applied as a working hypothesis as 

 a competitor of the older explanation for other portions of the Atlantic shores. 



THE SAND HILLS OF NEBRASKA^ 



About 20,000 square miles in central and western Nebraska, with smaller 

 areas in neighboring states (mostly between 2000 and 3000 feet above sea-level) 

 are characterized by sand-hills unlike those of any other part of the world. Pro- 

 fessor Pool has now written a comprehensive account of this region. His 

 monograph discusses the history of exploration of the area, its location and 

 extent, geology and soils, topography and drainage, climate, effects of fire, 

 soil moisture and texture, and plant "formations" and associations (this topic 

 covering nearly 100 pages), and closes with a bibliography and thirty excellent 

 half-tones. 



The region is underlaid by Tertiary sandstones, the weathering of which has 

 produced a soil consisting almost wholly of quartz sand on the uplands, with 



1 A Study of the Vegetation of the Sand-hills of Nebraska. By Raymond J. Pool. Map, ills. 

 ■Geol. & Nat. Hist. Surv. of Minnesota Botanical Studies, Vol. 4, Part 3, pp. 189-312. Univ. of 

 ^Minnesota, Minneapolis, 1914. 9)^ x 6]4. 



