BARRIS — OUR LOCAL GEOLOGY. 29 



coral reef, and resting on it both the limestones and shales of the Spir- 

 fer Parryanus beds, almost lost under the soil of the prairie. 



In the First Ravine the beds appeared in the bottom of the stream. 

 In this, they were only reached by a lengthy, tortuous route, and found 

 at the top of the hill from thirty to forty feet above the stream. 



The Third Ravine contains no exposures, but following a road west 

 of William Sauer's quarry nearly a quarter of a mile, a little stream is 

 encountered crossing the bluff, in two particulars differing from any of 

 the others we have noticed. It runs in an entirely different direction. 

 They from north to south to the river, this from west to east, making 

 a sharp angle to cross the bluff. It is the. only stream whose whole 

 course lies through the Spirifer Parryanus beds. For a quarter of a 

 mile exposures are frequent both in rock and shale. First appear 

 large, heavy, extended blocks detached from the bluff, usually sparing 

 of fossils. As we ascend the shales come into view. The channels 

 cut by the stream are unusually deep and crowded throughout the en- 

 tire depth with masses of broken shells of, mainly, Athyrus vittata. 

 Beyond these the hardened limestone is again seen till lost in the 

 prairie. The following section is given : 



FEET. 



Thick, heavy bedded limestone. ..... 4 



Shales, excessively fossiliferous. ...... 5 



Lower harder limestone. . ..... 3 



In the Fourth Ravine, generally known as the "Dodge Ravine," is 

 a remarkable exposure of these beds just north of the large quarry in 

 the Spirifer Pennatus beds. The encrinal limestone here attained its 

 utmost hardness and forms for some distance the smooth floor over 

 which the stream flows. Its width is forty or fifty feet and across it 

 had extended two or three strata of limestone a few inches in thick- 

 ness, filled with the casts of Spirifer Parryanus. The action of the 

 water had broken away all the central portions, leaving on both sides 

 of the stream projecting towards it these differing strata. The crowded 

 condition of the shells, their number, their exclusion of every other 

 form, calls to mind the description given by Prof. Calvin of casts of 

 the same Spirifer as found at Montpelier in a slightly differing rock.* 

 The locality has been worked by visitors who would naturally suppose 

 it to have been in the Spirifer Pennatus beds. Certain peculiarities 

 would favor such conclusion. The appearance of the Spirifer in such 



♦Geology o£ Iowa, Vol. I., page 45. 



