340 THE GEOLOGY OF MINNESOTA. 



rOtlena Hmetone. 



is mostly at this point a soft, clayey shale, with concretions and harder 

 laminated patches which are probably more calcareous, showing, parallel 

 with the curving and wavy laminae, rusty lines that are due to the arrange- 

 ment of the irony layers, or to the stoppage of iron in ferriferous water 

 that trickles through the rock. These concretions appear also in the lime- 

 stone on old surfaces, though not distinguishable on freshly broken sur- 

 faces.* 



The underlying limestone, which probably represents the strata that 

 have been well known as Galena limestone, has an exposed thickness in the 

 vicinity of High Forest amounting perhaps to forty feet. This is heavily 

 bedded, very firm and of a buff color, with cloudings of gray, and even 

 of blue on some of the deeply quarried beds, and a magnesian aspect. It 

 contains almost no fossils besides crinoidal stems, but shows rarely impres- 

 sions of a large Orthoceras; at other places it is non-fossiliferous, as at Gar- 

 rick's quarry. 



The same lime-rock appears more abundantly in the bluffs at Stewart- 

 ville. In the loose materials along the south bank of the stream, in the 

 vicinity of Stewart's mill, are found numerous specimens of Maclurea, of 

 which there seem to be two species, one of which is probably that of pro- 

 fessor James Hall, M. Bigsbyi,-]- although in a somewhat higher horizon than 

 the " buff limestone" of Mineral Point, in which that species has been found. 

 These are the same as found in the Galena limestone at Lime City, Fill- 

 more county. This limestone underlies Rock Dell and portions of Salem, 

 Rochester, High Forest and Pleasant Grove. It extends into Marion and 

 Orion, and even into Eyota, and westward into Kalmar. It may be seen in 

 Garrick's quarry, sec. 18, Rochester. Its lower and upper edges cannot be 

 accurately traced. 



In lithological character, this rock is a heavily bedded, buff dolomite, 

 fine grained, or coarse and porous. It contains often small pieces of iron 

 pyrites, which, by weathering, give it ferruginous stains. Lead has not 

 been found in place in the rock, but farmers sometimes find it isolated on 

 the surface, evidently left behind when the rest of the rock material was 

 weathered away. It often contains crystals of spar; sometimes irregular 



*83 Mower county report for further concerning this shale. 



tKeport of the superintendent of the \Visconin geological survey, Jan. 1, 1861. 



