IOWA, AND WAPSINONOX RIVERS. 85 
the white, brecciated limestone lies about twenty feet above the water. On Red 
Cedar River, 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 dolomitie 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 ora 
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 Hntrochites. 
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 
eray compact limestone, containing Terebratula reticularis, Orthis resupinata, Spirifer 
euruteines, Lithostrotion hexagonum, L. ananas, Favosites Gothlandica (var. F. basal- 
tica), Gorgonia retiformis(?), and a small species of Cystiphyllum. The quarry 
* This rock has the same lithological appearance as the Quarry Creek rock, which gave, by Dr. 
Shumard’s analysis, 42-1 per cent. of carbonate of magnesia. 
