134 



Cincinnati Society of Natural History. 



been seen in a number of places in the State.* They are 

 brought to view distinctly in the weathered and hardened 

 surfaces, since the homogeneous sand on fresh fractures seems 

 to constitute the entire rock, and no trace of these fossils is 

 visible to the eye. They appear at this place on a lower bench, 

 where the rock is hardened and reddened. They always run 

 perpendicular, and can be traced to a depth of two and a half 

 feet by the little furrows the} 7 cause on the face of the rock 

 after the breaking and sliding down of masses of the bluff. 

 This structure was first seen in this sandrock at the base of 

 Dayton's bluff, at St. Paul, and was ascribed to Cretaceous 

 lithodomous shells, but it is more likely to be due to some 

 marine vegetable, or to worm-burrowing, of Cambrian age. 

 By examining areas that have suffered different degrees of 

 exposure, there can be traced a connection from the actually 

 empty porous openings, through different degrees of exposure 

 and induration, including a simple annular spottedness, to an 

 innate internal structure in the mass of the rock itself. It 

 would be the same as if a multitude of horse-tail rushes, or 

 others, were growing in the bottom of the sea when the sand 

 was accumulating, and became gradually buried under the 

 sand, and then were imprisoned and fossilized, their presence 

 only being evinced now by the cementation of the sand-grains 

 about their exterior, or by a looseness of the same in their 

 interior, thus not only forming a rude cast of each stem 

 within the rock, but also providing for the more rapid erosion 

 and removal of the grains that may have reached within their 

 cases. The spots are only seen on upper surfaces, and if they 

 be not due to imprisoned rushes or stems of some sort, or to 

 worm-burrowing, they are at present inexplicable. They are 

 generally from an eighth to a quarter of an inch in diameter." 



This species the present writer has proposed to call Sco- 

 iithus minnesotensisf\ 



Similar tubes are noticed as occurring at Waterloo and 

 Beloit, Wisconsin.! In Illinois, in LaSalle County, || a pecul- 

 iar feature of the sandstone is noticed. It is stated to contain 



*" They are conspicuous at Castle Rock, in Dakota County." 

 fBull. Geol. Soc. America, Vol. Ill, 1891, p. 41. 



\ Chamberlin, T. C. Geology of Wisconsin, Survey of 1873-77, Vol. II, 1877, p. 

 288 ; also, Vol. I, 1883, p. 147. 



|| Geological Survey of Illinois, Vol. Ill, 186S, p. 280. 



