ROCK ISLAND COUNTY. 223 



Megiftocriniu latux, Synbathoerinm matutinw. Taj-ocrinu* interseapulariv, 

 I. (/radii*. Pentremites ftub-tru)icatu<i. Platyceras rentricosum, Astreospon- 

 gia Hamiltonensis, FenesteUa bifurcata Polypora Hamiltonemis, and Stria- 

 topora loicensis. There are also to be obtained from this division sev- 

 eral species of turbinated corals, and a Gomphoceras that have not as 

 yet been specifically determined. 



The upper division contains many of the species above named, and 

 in addition many corals belonging to the genera PhiUijisaxtrea and Stro- 

 ma topora. associated with CystiphyUum Americanum in great numbers. 

 There are also some brown beds near Andalusia that contain numerous 

 Gasteropoda and Orthoceratites, and a few miles below, these are overlaid 

 by from eight to ten feet of a brown magnesiau limestone that contains 

 casts of a large Spirifer like S. Parryantis and Strophomena demwsa. 

 These brown beds are directly overlaid near the mouth of Stonecoal 

 creek by the sandstones and shales of the Coal Measures. There can 

 be no doubt that the two upper divisions of this limestone fairly repre- 

 sent the organic forms of the Hamilton group as it appears in Xew York 

 and Canada, and as no fossils specially different from these have been 

 obtained from the lower bed, we see no good reason for assigning that 

 division to a lower formation. This group attains a greater thickness 

 here than at any other point in the State, and at the first outcrop of 

 this limestone to the southward, in Calhoun county, its entire thickness 

 scarcely exceeds ten feet. 



Xiagara Limestone. From Cordova to Port Byron this formation 

 outcrops heavily. Leaving Port Byron it gradually sinks as we ap- 

 proach Hampton, and a little south, of that place disappears beneath the 

 outliers of the Coal Measures. The stone at Cordova has a tough, horn 

 stone like consistency and appearance, unlike its outcrop at Fulton and 

 farther north. Some of its top layers break with a splintery fracture, 

 and the lines of stratification and bedding are very irregular. It has 

 some of these characteristics at Port Byron, but is more brecciated in 

 structure and yellow in color. Stems of encriuites, some of them half an 

 inch in diameter, fill some of the large blocks of limestone at this point 

 Following the bluff's from Cordova eastward and down to Pleasant Val- 

 ley, this limestone outcrops and is quarried in many places, both in the 

 face of the bluffs, and by digging into the higher bottom lau-1 between 

 the bluffs and the Maredosia slough. Its characteristics along this ea>t- 

 ern exposure of outcrop change a little. Minute dendritic spots or stare 

 give a speckled appearance on fresh fractures, and the color is a yellow 

 or reddish brown. The stone is softer, and occasional fragments of Pen- 

 tamer us ftblnnfinx are seen. All that upland region north of Pleasant 

 Valley is underlaid by this Niagara formation and a thin outlier of Coal 

 Measures, but the soils and upland clays deeply cover them, except 

 where the small streams cut down through the superficial deposits. 



