168 THE GEOLOGY OF MINNESOTA. 



[Dolomitic limestones. 







sian limestones, has sometimes made it pass fora sandstone. It has a light 

 and lively color, and in that respect it has the advantage of the darker- 

 colored stones. As a material for building it is a little surprising that this 

 formation has not been more employed. It occurs in fine exposure in the 

 western part of Goodhue county, abundantly in Dodge county, as well as in 

 Olmsted and Fillmore, along the streams, and can be wrought extensively. 

 It not only furnishes a building material that is suitable for all ordinary 

 uses in foundations and abutments for bridges, but it also cuts easily to a 

 regular and smooth surface. Its bedding is sometimes heavy, reaching two 

 or three feet in thickness, and the stone is strong enough to endure both 

 pressure and long weathering. 



At Mantorville the quarries are owned by Mr. H. Hook, P. Mantor, 

 A . Doig, and others. Mr. Mantor's was opened in 1856, and Mr. Hook's in 

 1866 ; Mr. Doig's in 1870. This is one of the oldest quarrying localities in 

 the state, and much stone from here had been hauled over the country, 

 before the construction of railroads, to Rochester and other towns. It has 

 been employed at Mantorville in the construction of Wright's hotel, the 

 county court house, and a couple of churches. At Rochester, Cook's block, 

 the court house, the public school house, and the state insane asylum, are 

 all faced or trimmed with the Galena from Mantorville. 







It will be seen by the general table that dolomitic limestones are also 

 found in the Trenton formation, underlying the Galena, and that they are 

 quarried at Minneapolis. They are Nos. 22 and 24. It is probable that this 

 character pervades certain beds of the Trenton on about the same horizon 

 at points further south, but they have not been detected, although there is, 

 even in the blue and argillaceous beds of the Trenton generally, a small per- 

 centage of magnesia. These magnesian strata are not those usually employed 

 and desired for construction, but they are for the most part avoided in build- 

 ing, or are put in the interior and protected portions of the walls at least 

 the stone represented by No. 22 is so treated, while No. 24 is used indis- 

 criminately with No. 27 at the same place. The position of these magnesian 

 strata in the Minneapolis quarries may be seen by examining the following 



General descending section of the Trenton at Minneapolis. 



1. Dolomitic limestone (No. 22 of the general table) with considerable argillaceous matter, 

 crystalline, rough to the touch, hard but splitting lenticularly under the weather. This has a 



