HARRIS OUR LOCAL GEOLOGY. 3 1 



city are exposed on both sides of the river, cidminating in thickness 

 and interest in the Cook and neighboring quarries, and disappearing a 

 short distance below. They are of comparatively limited extent, con- 

 fined within two or three miles and reaching a height of about twelve 

 feet. They contain characteristic fossils to the number of twenty-four. 

 Eight pass into the beds above, while about the same number are 

 undetermined. 



The Spirifer Pennatus beds appearing in the old LeClaire quarry 

 are seen on both sides of the river and are in full force throughout the 

 Ravine region, disappearing for a time with the exposure in the Sixth 

 Ravine. Of greater extent than either of the other beds, they appear 

 through the distance of eleven or twelve miles and in height range 

 from sixty to seventy feet. About sixty species of fossils have been 

 found in these beds, while but one of them is represented in the suc- 

 ceeding beds and eighteen are undetermined. 



The Spirifer Parryanus beds are not found through the distance of 

 seven or eight miles below the city, and then only in patches in the 

 First and Second Ravines. They are well exposed on the little stream 

 between the Third and Fourth Ravines, carrying all their peculiar 

 characteristics into the Sixth Ravine, beyond which they soon disap- 

 pear. Their extent is about four miles, their height from twelve to 

 fifteen feet. Described fossils are limited to five, while two are unde- 

 termined. 



As to the place of these beds in the Geological formations of the state, 

 it will be remembered that the Devonian of the State of New York 

 embraced four large Geological formations. It was natural to suppose 

 that in its extension westward some of these formations would again 

 appear. As early as the Second Geological Survey, Prof. White took 

 the ground that all the Devonian strata of Iowa evidently belonged to 

 a single epoch, undoubtedly referable to the Hamilton period, as 

 recognized by t^e New York geologists.* After long, patient study. 

 Prof. Calvin came to the same conclusion. As one of the results of 

 his labors he separated all the calcareous beds of the Iowa Devonian 

 into three divisions. The first he named the Lime Creek Shales, the 

 second the Cedar Valley Limestone, the third the Independence Shales. 



It is to the middle division, " the great limestone series," that the 

 beds described in this paper belong. The writer has directed atten- 

 tion simply to a study of its most easterly outcrops, trusting his work 

 may be of some use to the student in his geological studies. 



♦Geology of Iowa, White. Vol. I., page 187. 



