CHAPTER V. 



1. CRETACEOUS SYSTEM* 



EAKLIEB CRETACEOUS. 



There being no rocks in Iowa of either Permian, Triassic, 

 or Jurassic age, the next strata in the geological series which 

 we find belonging above the Upper coal-measures, are of Cre- 

 taceous age. They are found in the western half of the State, 

 and rest unconformably upon the strata beneath them. They 

 do not partake of the dips and undulations of those upon 

 which they rest, and which have been described in the preced- 

 ing pages, but have a general dip of their own to the north of 

 westward. This dip, however, is slight, and probably has 

 nowhere a greater angle than the average slope of the 

 surface of the country in the opposite direction which lies 

 between western Iowa and the base of the Rocky mountains. 

 Indeed, it seems probable that the disappearance of the 

 palaeozoic rocks beneath those of Cretaceous age is fully as 

 much due to the slope of the surface from that direction as to 

 an actual dip of the strata from a horizontal line in the 

 opposite one. So far as is known to the writer, Dr. D. D. 

 Owen was the first to publish the fact of the existence of 

 Cretaceous strata in Iowa. Subsequently, the extensive 

 deposits of that age, which exist along the valley of the 

 Upper Missouri river, of which ours are a part, received the 

 most extensive and detailed exploration that has yet been 

 given to them, by Messrs. Meek and Hay den. 



In 1863, this region was visited by Prof. Jules Marcou, and 



* The term "system" is applied to the Cretaceous, in conformity with the plan of 

 classification explained in the introduction. 



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