HOUSTON COUNTY. 225 



St. Croix sandstone.] 



sandstone layers is mainly turfed over so as to render an inspection of their 

 contents impossible except at points near the top and near the bottom. 

 There is a line of nearly constant exposure about forty feet below the top 

 of the St. Croix, occupying an interval of thirty or forty feet, which is particu- 

 ticularly noticeable along the north side of the river, and is again mentioned 

 in the report on Fillmore county. There is another exposure of these beds 

 near the level of the river at the dam at Houston. The former consists of 

 a hard, firm sandrock, and the latter is soft and crumbling, with cross strat- 

 ification. Above the line of constant exposure, about twenty-five feet, is a 

 blind terrace which occasionally reveals the rock which causes it. It is a 

 sandstone, and is included in the foregoing thickness of 420 feet. 



At one mile north of Sheldon there is an apparent dip in the outcrop- 

 ping upper edge of the St. Croix, as it strikes across the bluffs. Its direc- 

 tion is perhaps a little west of south, and amounts to two or three degrees. 

 It is entirely local, and the corresponding upward dip in the opposite di- 

 rection is invisible. The bluffs south and north have their usual hight.* 

 No such dip was noticed in any other part of Houston county, but it is 

 very likely this is on the strike of the noticeable disturbance in these for- 

 mations which has been mentioned by the geologists of Iowa as occurring 

 in the bluffs of the Mississippi river at McGregor and Lansing, in the state 

 of Iowa. 



In section 2, Caledonia township, the following section was taken : 



Section covering the junction between tlie St. Croix and the St. Laiwenee. 



Feet. 

 Slope, covered with large blocks of limestone, ----- 200300 



Even layers of limestone, quarried, 12 

 Hid, mainly limestone, like the next, - 40 

 Limestone, with broken and curling bedding, cherty, arenaceous or massive, with some green- 

 sand, - - 25 

 Lime and sand, lumpy with irregular concretions, mainly massive, - 15-20 

 Soft sand, witli cemented or quartzitic lenticular lumps, 10 

 Soft, massive sand, (causes the blind terrace at Houston), 25 



The line of constant exposure mentioned as occurring at Houston, near 

 the top of the St. Croix sandstone, lies below this section. This line is 

 more evident in the north than on the south bluffs, due, probably, to the 

 erosive action of the prevailing winds which are from the southwest, and 

 to the greater scarcity of timber on the north bluffs as already noted under 

 the head of Soil and Timber. 



'Compare Geoloey of Iowa. Hall & Whitney, 1858, Part I., p. 51; and the Wmona county report, where a similar dip 

 is described in the Shakopee and St. Peter. 



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