GRASSES OF IOWA. 369 



later sandstones and limestones of the Paleozoic were laid down in 

 the great basin between these two ancient land masses. As the 

 whole of northwestern Iowa has been buried beneath the Cretaceous 

 beds which were laid down over the upturned and eroded older 

 strata, the beds next in age to the quartzite are found in the extreme 

 northeastern part of the state, where they lie on the flanks of the Wiscon- 

 sin land. From the northeast to the southwest, successively younger 

 strata are found in parallel and concentric belts, from the Cambrian 

 through the Upper Carboniferous. As pointed out by Norton- these 



Pig. 256. Jasper pool in Lyon county. The bluffs are formed of Sioux quartzite. 



beds lie with a gentle southward inclination and, in the north, sag toward 

 a line approximately marked by the upper Des Moines river. To the 

 southwest the beds lie approximately level, and, in the southwest and 

 again at Ames, the lower beds rise in a dome which is concealed below 

 the later beds. From Cambrian to Carboniferous the different forma- 

 tions of the Paleozoic occur in regular sequence. The presence of out- 

 liers indicates an occasional overlap, and retreating cliff erosion. In the 

 western portion of the state the Cretaceous is found, laid down evidently 

 after a considerable erosion, and resting indiscriminately on all the mem- 

 bers of the Carboniferous. 



*Iowa. Geol. Surv., 6: 137. 

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