IOWA, AND WAPSINONOX 



RIVERS. 



83 



the white, brecciated limestone lies about twenty feet above the water. On Red 

 Cedar Eiver, half a mile from Rochester, is magnesian limestone like that at Park- 

 hurst, and a variety of freestone is again in close proximity ; and half a mile west 

 of the same place, twenty feet of buff-coloured earthy magnesian limestone* is 

 exposed, with nests of calcareous spar and black specks disseminated, such as are 

 found at the head of the Upper Rapids of the Mississippi. 



On Rock Creek, a mile northeast of Rochester, a light^coloured magnesian lime- 

 stone is in place ; and the same rocks form ledges of thirty-five feet above the level 

 of Rocky Run, on Section 27, Township 80 north, Range 3 west. At these latter 

 localities the magnesian limestone is of a much lighter colour than is usual ; it has, 

 however, the texture and glistening aspect peculiar to the dolomitic rocks. Only 

 obscure casts of organic remains are found in it. 



In digging a well on Section 9, Township 80 north, Range 3 west, rock was 

 struck at thirty-two feet, and the excavation continued for forty-three feet more, 

 first through white, close-grained limestone, and then magnesian limestone. The 

 ' top of the well is about seventy feet above the waters of the Cedar. A mile or a 

 mile and a half from this place, on Rocky Run, earthy magnesian limestone with 

 dark specks is exposed eight feet above the water. At the south end of Mason's 

 Grove, the rock is a cellular magnesian limestone, containing Entrocliites. 



Between this place and Rocky Run, porphyritic boulders are scattered over the 

 prairie, of a similar composition to those observed in the Winnebago Reserve, but 

 smaller : about one-third the size. 



At the crossing of Clear Creek, in the southern part of Cedar County, twenty-six 

 feet of buff-coloured magnesian limestone, with cavities, is exposed in a quarry. 

 The lower strata, to the height of fifteen feet, lie in heavy beds from one and a half 

 to three feet thick ; the next foot is composed of layers of from one to three inches 

 thick, and over the whole the beds are much broken, and irregularly divided. 

 Were it not for the cavities in the thick beds, a good building material might be 

 obtained at this locality. 



At the crossing of Breakneck Creek, on the road from Rochester to Marion, the 

 rocks are schistose, even-bedded, and ring under the hammer, possessing a texture 

 like some of the Davenport limestone. 



On Section 11, Township 83 north, Range 7 west, of the 5th Principal Meridian, 

 west side of Indian Creek, the upper rock is compact, close-textured limestone, 

 resting on magnesian limestone beneath. 



At the source of the Big Spring, that drives M'Leod's Mill, on Section 9, Town- 

 ship 83 north, Range 7 west, a partial exposure is seen of soft, yellow, magnesian 

 limestone, like that observed at Quarry Creek, near Parkhurst. 



The bed of Cedar River, at the rapids in Linn County, is formed of white and 

 gray compact limestone, containing lerebralula reticularis, Orilds resnpinata, Spirifer 

 euruteines, Lithostrotion hexagonum, L. ananas, Fcwosites Gothlandica (var. F. basal- 

 tica), Qorgonia retiformis (?) , and a small species of Cystiplvyllum. The quarry 



* This rock has the same lithological appearance as the Quarry Creek rock, which gave, by Pr, 

 Shumard's analysis, 42-1 per cent, of carbonate of magnesia. 



