600 REVIEWS 



Finch, G. E. A Terrace Formation in the Turkey River Valley, Fayette 

 County, Iowa. Proc. Iowa Acad. Sci., Vol. VIII, pp. 204-6, 1901. 

 The terrace is in a valley that heads in the drift covered, but passes into the 

 driftless region of northeastern low^a. The material found in the terrace is shown in 



the following section : 



Feet 



1. Surface soil of loess-like character ....---.- 2-3 



2. Limestone fragments with a few glacial pebbles and with inclusions of blocks 



of loess ..-----....--- 6 



3. Loess-like material with soil at top --------- 8 



4. Iron-stained pebbly bed largely of local rocks, but containing green stones 



and quartz pebbles 3 



Leverett, Frank. Old Channels of the Mississippi in Southeastern Iowa. 



Ann. of Iowa, Vol. V, pp. 38-51, Des Moines, 1901. 



After calling attention to the several stages of glaciation that have influenced 

 the course of the Mississippi, an attempt is made to outline the course the river took 

 durini^ each glacial stage. 



Leonard, A. G. Geology of Wapello County. Iowa Geol. Survey, Vol. 



XII, pp. 439-99. 1902. 



The physiography is discussed on pp. 443-48 ; the Pleistocene deposits, on pp. 

 472-75, and water supply and soils, on pp. 496-99. The part of the county northeast 

 of a line running through Kirkville, Dahlonega, Agency, and Ashland is less deeply 

 eroded than that southwest of it, but the entire county was originally a drift plain 

 sloping southeastward. This difference in topography is explained by the relation to 

 river systems and resulting gradients. The deeply eroded part is tributary to the 

 Des Moines River, whose course to a given point on the Mississippi is more direct and 

 the gradient steeper than that of Skunk River, which drains the less deeply eroded 

 northeastern part. Attention is called to the greater width of the valley when in the 

 soft Coal-measures than it is in the more resistant St. Louis limestone, the propor- 

 tionate width being as 5 to 3. The Des Moines appears to be a re-established stream 

 along a preglacial line. Its selection of the old course is thought to have been brought 

 about by an incipient sag produced by the greater settling of material where the drift 

 is very thick, an idea earlier brought out by Bain.^ 



The average thickness of the drift in this county is estimated to be not more than 

 100 feet, but the maximum may reach 200 feet. The county is entirely outside the 

 limits of later drift sheets than the Kansan, though that drift is capped by a few feet 

 of loess apparently of lowan age. The surface of the Kansan drift is deeply weath- 

 ered for 10 to 12 feet below the base of the loess. 



MacBride, T. H. Geology of Clay and O'Brien Cotmties. Iowa Geol. 

 Survey, Vol. XI, pp. 461-508, igoi. 



The physiography is discussed on pp. 463-82; the Pleistocene geology, on pp. 

 482-89, economic products, on pp. 491-98, and forestry notes, on pp. 498-508. As 

 these counties lie almost wholly within the limits of the Wisconsin drift, the drainage 

 is very immature, and the chief contrasts in topography are such as are afforded by 

 moraine and drift plain. The morainic topography is very largely comprised in the 



^lowa Geol. Survey, Vol. VII, p. 280, 1897. 



