40 IOWA ACADEMY OF SCIENCES. 



described beds in situ, in Guthrie and some of tlie southwestern counties 

 and set them down as Cretaceous. To those in Montgomery county, con- 

 sisting of almost wholly of ferruginous grits, he gave the name Nishnabotna 

 sandstone. The exposures farthest to the southeast were located in Guthrie 

 county; the southernmost at Red Oak, Montgomery county. These are all 

 described as outliers, the distance from the assumed eastern and southern 

 limits of the mam Iowa Cretaceous deposits, of which the Sioux City beds 

 form by far the most important adjunct, varying from twenty to nearly one 

 hundred miles. In individual size these outliers have been considered as 

 only a few miles, perhaps one to less than twenty, in their greatest diameter. 



During the field season which has recently closed a cousidei'able amount 

 of work was done in southwestern Iowa; additional information pertaining 

 to the Cretaceous outliers in general, was secured; the southern limit was 

 extended and conclusions pertaining to areal mileage of the different 

 outliers have been drawn with greater or less satisfaction. 



In the first place let the topography of southwestern Iowa be considered 

 briefly. Eastward from the bluffs which are pi-evalent along the great 

 flood plain of the Missouri or adjacent to the river itself the counties 

 consist of gently rolling uplands, which rise gradually to a height of one 

 hundred to two hundred feet above the near by waterways. The tops of the 

 ridges between the usually parallel streams continue in their axial lines in 

 an almost unbroken plane for many miles. The bottom, level land next to 

 the larger streams varies in width from a few yards to one or two miles, 

 this width depending largely upon the size of the stream which penetrates 

 the low land. From the outer margins of these bottoms there rise gradual 

 slopes curving smoothly to the upland drainage lines. Occasionally are 

 found outcroppings of bedded rock in these slopes but they are in no wise 

 extensive in any locality. There are, however, in western Iowa beds of the 

 Coal Measures which are exposed, but rarely are any such beds exposed at 

 a great distance above the streams near which they are situated. The top 

 of many are but a foot or so above the water, others fifty or possibly more; 

 but those approximating the former in extent predominate. In the vicinity 

 of the Cretaceous outliers this is even so and such occurrences would 

 undoubtedly indicate if not certainly prove that these inland streams have 

 cut through friable beds of the Cretaceous and but only a few of the upper 

 beds of the hard Coal Measures, that possibly not unfrequently has the 

 former formation not been passed through by the streams now existing 

 and some of the so-called outliers are connected and not separated as here- 

 tofore supposed. The fact that the drift, though omnipresent, in this sec- 

 tion of the State is not excessively heavy, not heavy enough to hide pre- 

 cipitous limestone bluffs, if they be of considerable thickness, makes this 

 state of affairs moi'e plausible. This condition seems even more probable in 

 parts of Guthrie county where the bottom lands are much narrower than 

 those to the southwest. Again, it is quite possible that these outliers in 

 Montgomery and adjoining counties extend farther northward and those in 

 Guthrie county farther northwestward, towards the sources of and between 

 the streams along which they lie; at the same time shortening the space 

 intervening between the outliers and the present limits of the main Cre- 

 taceous body in Iowa. Although no positive information can be given in 

 support of this theory, the exposures being few in number and only adjacent 



