BUILDING STONES. 



Dolomitic limestones.] 







and Albert Lea, also in the jail at Blue Earth City, and in the state normal 

 school and the city schools at Mankato. 



Besides the analyses given in the general table, of the Shakopee lime- 

 stone, which show a high per cent, of insoluble matter, the following may 

 be added from the same formation taken five miles below Mankato from 

 layers burned for quicklime by Mr. Geo. C. Clapp. These layers are in the 

 very top of the Shakopee, and are slightly fossiliferous and gray with 

 remains of organic matter. 



Insoluble, 2.82 



Ferric and aluminic oxides, 1.39 



Calcium sulphate, - 6.74 



Calcium carbonate, 52.22 



Magnesium carbonate, - 36.04 



Total, - - 99.21 



The dolomitic limestone quarried at Mantorville, in Dodge county 

 (No. 20), is from the Galena formation, which lies near the top of the Lower 

 Silurian, separated from the Mankato and Easota quarries by a thickness 

 of over 300 feet of strata. This formation has quite an extensive area in 

 the south-central part of the state, and is also quarried at several other 

 places in Dodge, Olmsted, Mower and Fillmore counties. While this stone 

 is not so strong under pressure as the dolomites and dolomitic limestones 

 already mentioned, it possesses such an average of other good qualities, ' 

 having no especially weak point in its character, that it ranks well with 

 them, and at the same time its resistance is sufficient to warrant its use 

 in all ordinary construction. Its usual color is buff', although on deep and 

 fresh quarrying it also shows that its normal color, like most other lime- 

 stones, is blue. Its texture is open, even porous, with minute cavities. In 

 some of its beds, which, however, are not wrought except for the heaviest 

 and roughest masonry, it exhibits large cavernous patches with a rough and 

 forbidding aspect. These, however, are not common, the sedimentation 

 having been generally so undisturbed by chemical or mechanical agencies 

 that the layers are regular and continuous, and the texture uniform through- 

 out large tracts. Minute crystals of brown spar often line the cavities. It 

 also sometimes embraces iron pyrite, which, weathering out, stains the face 

 of the rock with rust of iron. The grain is crystalline, and sometimes gran- 

 ular. This granular texture, which is also frequently seen in other magne- 



