REVIEWS 60 1 



eastern range of townships of Clay county. There are wide tracts of plane-surfaced 

 gravel outside of this moraine, and the gravel is found to be covered by a loess 

 deposit that must be younger than the loess of the eastern part of the state, which is 

 correlated with the lowan drift-sheet. The thickness of the drift in these counties is 

 remarkable. A well at the county farm in O'Brien county, east of Primghar, is 

 reported to have reached a depth of 700 feet, nearly all blue clay, and a well on the 

 Boyd farm in Caledonia township, said to be 1,000 feet deep, is through the blue clay 

 nearly all the way. The altitude of the drift surface at these wells is about 1,500 feet 

 above tide. 



MacBride, T. H. Geology of Cherokee and Biiena Vista Counties. Iowa 



Geol. Survey, Vol. XII, pp. 303-53, 1902. 



The physiography is discussed on pp. 306-16; Pleistocene deposits, on pp. 316- 

 38 ; soils, clay industries, gravel, and water supplies, on pp. 338-43, and forestry notes 

 on pp. 344-53. The contrasts in topography of the Wisconsin and the older drift of 

 that region are clearly brought out. The drift, which in the report on Clay and 

 O'Brien counties, was thrown into the Wisconsin, is here considered a possible early 

 Wisconsin, while that bordered by the Altamont moraine is thought to be the proba- 

 ble limits of the I. ate Wisconsin. Further data are presented concerning the great 

 thickness of drift in that region. A well at Marcus in the western part of Cherokee 

 county, on ground standing 1,455 feet above tide, reached a depth of 680 feet without 

 entering rock. This well is outside the limits of the Wisconsin drift. 



Miller, B. L. Geology of Marion Cotmty. Iowa Geol. Survey, Vol. XI, 



pp. 127-97, 1901. 



The physiography is discussed on pp. 1 31-40; Pleistocene deposits, on pp. 163- 

 69; water supplies, on pp. 193-96; soils, on pp. 196, 197; the remainder of the 

 report being devoted to the hard-rock geology. This county is outside the limits of 

 the lowan and Wisconsin drift-sheets, and has the topography of an eroded drift 

 plain such as characterizes the Kansan drift elsewhere. The South Skunk and Des 

 Moines Rivers are apparently re-established along the course of preglacial valleys. 

 The remainder of the drainage is largely in new lines. It is noted that the streams 

 have a tendency to flow along the base of the south bluff, and in explanation two 

 causes are given, one being the influence of the rotation of the earth, brought to notice 

 by Gilbert, the other the different rates of decomposition of rocks on the two sides, to 

 which Calvin has given the preference in earlier reports of the survey, it being thought 

 that freezing and thawing alternating rapidly on the north side of the valley break up 

 particles, so that they are more easily transported into the valley than on the more 

 shaded and longer frozen south side. Another cause brought out by John T. Camp- 

 bell in 1884 is not considered.' This explains the low inclination of south-facing 

 drift slopes to the creeping of the deposits on those slopes, which is favored by their 

 deposition by a south-flowing current of ice. 



Norton, W. H. .Geology of Cedar County. Iowa Geol. Survey, Vol. XI, 



pp. 279-396, igoi- 



The physiography is discussed on pp. 284-300 ; the Pleistocene deposits, on 

 pp. 343-77 ; soils, on pp. 389-96. The lowan and Kansas drift plains present 

 marked contrasts in amount of erosion in this as in other counties of eastern Iowa. 



'Am. Nat., Vol. XVIII, 1884, pp. 367-79. 



