650 ABSTRACTS 



limestones composing it stand at a high angle, not as a result of fold- 

 ing but because of the conditions of deposition which seem to have 

 been much the same as lead to cross-bedding in sandstones. Below 

 the Le Claire is the reef rock of the Delaware, while above are the 

 fine-grained building stones of the Anamosa. The drift deposits of 

 the county include the Kansan and lowan drift sheets, certain water- 

 laid interglacial beds, the loess and the alluvium. Jones county is 

 near the drift border and the puzzling anomalies of topography char- 

 acteristic of that region are well developed. 



In Boone county Dr. Beyer treats a region lying wholly within the 

 Coal Measures and wholly within the area covered by the Wisconsin 

 drift. The newness of the topography, which has been developed in 

 post- Wisconsin time is striking. The Des Moines river runs through 

 a deep narrow trench which follows the crest of a preglacial ridge. 

 The appearance of the Gary moraine is well shown in Plate IV and 

 the area covered by it is indicated on the map of the superficial 

 deposits of the county which is the first drift map published by the 

 Iowa Survey. 



Warren county also is underlain entirely by the Coal Measures. In 

 several detailed sections across the county Professor J. L. Tilton has 

 illustrated their lithological character and structure. They are 

 covered by the Kansan drift, which is in turn mantled by the loess- 

 silt of southern Iowa. The main rivers of the county are considered 

 to be of preglacial age. North Middle and South rivers are thought 

 to have originally flowed southwest into the Cretaceous sea. They 

 were reversed by the post-Cretaceous earth movements and now drain 

 into the Des Moines, a subsequent stream developed along the strike 

 of soft strata. 



In Woodbury county there are exposures of the Cretaceous, includ- 

 ing the Dakota and Colorado, certain sand beds called the Riverside 

 sands and which, while of uncertain age, are considered to represent 

 the "latest Pliocene or earliest Pleistocene," the Kansan drift, the loess 

 and the alluvium. The Cretaceous beds have an important historical 

 interest, and the loess is of great thickness and quite characteristically 

 developed. Certain interloessial beds of drift are interpreted as the 

 result of berg ice and considered as indicative of a close relationship 

 between the loess and the Wisconsin ice ; a relationship which later 

 studies in adjacent regions do not seem to confirm. 



The studies in Washington county are a continuation of those 



