176 THE GEOLOGY OF MINNESOTA. 



[Sandstones. 



Most especially if it be on edge, and in a projecting cornice or capital, it is 

 a source of weakness to the structure, as well as of danger to all passers, 

 from the dropping of sheets or fragments as the weather by wet or frost 

 separates them from each other. The color of the Trenton makes it very 

 suitable for foundations, and for the ranges below the water-table, but even 

 there it should be well bedded in mortar and protected by the water-table 

 in order to keep out the water. 



The limestone quarried at Clinton Falls, near Owatonna, in Steele county, 

 belongs to the Lower Silurian. It is from strata higher than the Trenton 

 as seen atFaribault, and has been parallel! zed with the Hudson River form- 

 ation. The strata are from two to six inches in thickness and are broken 

 by frequent joints. The stone is of a bluish-drab color, and uniform char- 

 acter of texture. It is useful for common construction, but owing to the 

 thinness of the bedding it cannot be used for first-class buildings and heavy 

 masonry. It is associated in the stratification with much shale, and the 

 stone itself is affected by considerable argillaceous matter, which causes it 

 to be damaged by freezing and thawing, and by corroding vapors in some- 

 what the same degree as the Trenton stone at St. Paul and Minneapolis. 

 The shale, however, is minutely disseminated throughout the rock, instead 

 of being in lenticular interlaminations as in the Trenton. The chief quarry 

 is owned by Messrs. Lindersmith & Son, and its product is principally used 

 at Owatonna, and in the surrounding country. 



Microscopic characters of No. 29. In thin section under the microscope this has very much 

 the same appearance as No. 26, but has a few distinctly formed crystals of calcite porphyritically 

 distributed. 



6. SAJSTDSTONES. 



The stone quarried at Hinckley in Pine county, by the St. Paul and 

 Duluth railroad (No. 30), bears so strong a resemblance to that quarried near 

 Fort Snelling in Dakota county (No. 31), by the Chicago, Milwaukee and 

 St. Paul railway, both in general outward appearance and in its chemical 

 and physical characters, that it may on these grounds be supposed to belong 

 to the same formation. And since there are no stratigraphical nor struc- 

 tural difficulties opposed to such a reference, but rather evidences of such 

 irregularities as to require it,* they are here considered as belonging to the 



See tenth annual report, 1881. Geology of a deep well at Minneapolis. 



