8 IOWA ACADEMY OF SCIENCES. 



of saurians related to Plesiosaiirus, teleost fishes, and, in the uppermost 

 beds, impression of Inoceramus. At the summit of the column, overtopping 

 shales and sandstones alike, are the calcareous beds to which allusion has been 

 made. These consist, in part, of soft, chalky material and in part of more indur- 

 ated, though still soft, beds of fissile limestone that divides under the hammer or 

 on exposure to the weather, into relatively thin laminae crowded with detached 

 valves of Inoceramus problematiciis Schlot. 



In the portion of the section between the massive sandstone and the saurian- 

 bearing shale the beds are not everywhere constant. In some places they contain 

 thin bands of ferruginous concretionary sandstone. At Riverside, for example, and 

 at the works of the Sioux Paving Brick Co., there is a mass of rather thin bedded 

 calciferous sand-rock in the upper part of this division, developed to a thickness 

 of eighteen feet. 



A generalized section of the beds along the bluffs facing the Big Sioux river, 

 omitting some minute details and averaging local peculiarities of certain beds, 

 would be, beginning at the bare of the series: 



1. Irregular beds of sandstone varying in color and texture and inter- 

 stratified with thin beds of shale 18 ft. 



2. Grayish and mottled shales with thin ferruginous bands and arenaceous 

 layers 12 ft. 



3. Massive sandstone, mostly soft; but in places containing large concre- 

 tionary masses several teet in diameter in appearance and hardness 

 resembling quartzite 10 ft. 



4. Shales with usually two, but sometimes more, well marked thin bands 



of ferruginous concretionary sandstone (" Buttons" of the clay workers) 16 ft. 

 .5. Band of impure lignite 4 to 6 inches. 



6. Blue, yellow and red mottled clays (terra cotta clays), with selenite crys- 

 tals and some streaks of sand 30 ft . 



7. Argillo-calcareous or arenaceo-calcareous beds with much selenite (vary- 

 ing with locality) 20 ft. 



8. Shales more or less unctuous to the feel, somewhat variable in color and 

 texture, containing -remains of saurians and teleost fishes, the upper 



beds sometimes bearing impressions of Inoceramus prohlematicus 40 ft. 



9. Calcareous beds consisting of chalk and soft, thin bedded limestone, con- 

 taining shells of Inoceramus prohlematicus, Ostrea congesta, and teeth 



of Otodns, Ptychodus and other selachians 30 ft. 



Beds that are quite constant and easily recognizable in the region about the 

 mouth of the Big Sioux river are No's. 3, 4,5, 8 and 9. These, either singly or 

 collectively, become the guides whereby the beds of the several exposures may be 

 correlated. The deposits were traced up the Big Sioux valley for a distance of 

 forty miles; they were followed up the Missouri river as far as Yankton. 



In addition to the deposits exposed on the Big Sioux, Dr. C. A. White, under 

 the name of the Nishnabotna sandstone, refers to the Crttaceous age a series of 

 sandstones developed to a thickness of 100 feet along the river valleys in Mont- 

 gomery, Cass, Gruthrie and Greene counties. Referring to the work done by Meek 

 and Hayden on the Cretaceous deposits along the Missouri river, and noting the 

 names employed by these authors to designate the various sub-divisions of their 

 "Earlier Cretaceous," Dr. White* says: "The Cretaceous strata, of Iowa, have 

 so slight a development in comparison with those farther up the Missouri river 



♦Geology of Iowa, Vol. I., p. 288, 1870. 



