(;:,(-, THE GEOLOGY OF MINNESOTA. 



[St. Peter sandstone. 



durable than the blue, but is not so advantageously quarried in blocks of uniform thickness and 

 size. 



Farther southwest from Faribault, across the creek that enters the Cannon river from the 

 south near the fair ground, the Trenton evidently exists. This is evinced by the contour and 

 abruptness of the bluffs. The southern part of Warsaw and probably of Morristown, are thus 

 underlain by the Trenton. 



The Trenton has been quarried in the bank of the river below the Walcott mill, from six to 

 ten feet above the water. Above the dam this limerock formerly appeared in the bed of the river, 

 but it is now covered by the water of the dam, the water-power being due to the passing of the 

 river over this rock-horizon, the same as at the falls of St. Anthony. Stone from below the dam 

 was used in the bridge piers, and in the building of the dam. Quarries are owned by Henry Hall 

 and Gale Sexton. There is a small area of the Lower Trenton on the west side of the Cannon 

 river in sees. 33 .and 34, Bridgewater; and also in sec. 35, immediately west of St. Olaf 's college, 

 near Northfield. 



The St. Peter sandstone begins to be seen in the banks of the Straight 

 river about four miles north of the Steele county line, and at Faribault it 

 reaches a hight above the river of eighty feet according to the following 



Section at Faribaull in the right bank of the Cannon river. 



1. Drift (water deposited) covering occasional exposures of the Trenton lime- 



stone, and one or more beds of green shale 26 ft, 4 in. 



2. Shaly bedded St. Peter sandstone 3ft. 6J in. 



3. Massive St. Peter sandstone 76 ft. 7J in. 



Total 106 ft. 6 in. 



The St. Peter sandstone, having a thickness altogether of about 115 

 feet, rises about 110 feet above the river, west of Cannon City. It is ex- 

 posed at the Cannon Valley roller mill, S. E. J sec. 8, Cannon City, in a per- 

 pendicular wall, in the west bluff of a conical isolated hill, and affords there 

 a good opportunity to measure its thickness, since the river must be run- 

 ning very near the top of the Shakopee limestone. The top of this hill, 

 though covered sparsely with a pebbly loam, is strown with bits of limerock 

 due to the demolition of the Trenton in situ. 



Fossils in the St. Ptter. The sandrock here is pitted with circular holes, such as have 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 the deptli of two and- a half feet by the little furrows they 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 Cam- 

 brian 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 ex- 

 posure 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 



'They are conspicuous at Castle Rock, in Dakota county. 



