450 THE GEOLOGY OF MINNESOTA. 



[Hydraulic cement. 



Lime, CaO 38.53 



Magnesia, MgO 22.73 



Ferric oxide, Fe 2 O 3 , 4.71 



Silica, SiOi 16.24 



Alumina. A1 2 O 3 5.35 



Potassa, K 2 O ' 1.81 



Soda, NajO 0.57 



Water, II 2 O '. 0.51 



Carbonic acid, CO.. 9.26 



99.71 



This company, beginning operations here in 1882 and 1883, have erect- 

 ed extensive buildings for carrying on the business, using the same rock in 

 their construction. The Shakopee formation at this place has a different 

 grain and texture from the strata seen at the quarries in the north part of 

 Mankato and elsewhere.* 



It seems to have more nearly the characters of the lower part of the Shakopee limestone 

 quarried by J. K. Beatty & Co. in section 20, Lime, which on analysis showed a similar compo- 

 sition, being reported by Prof. Dodge as follows:! 



No. 74. Rock a siliceous limestone. Digested with hydrochloric acid, a residue was left, 

 amounting to 19.67 per cent. The dissolved portion was therefore 80.33 per cent. 



Analysis of portion dissolved by hydrochloric acid: 



SiOi 27 per cent., being .21 per cent, of whole rock. 



AljOj 15 " " " .11'" " " " " 



Fe a O 3 3.03 " " " 2.43 " "'" 



CaOCO 2 o5.62 " " " 44.68 " " " 



MgOCOi 39.13 " " " 31.59 " " ' 



98.20 79.02 



Analysis of portion not dissolved by hydrochloric acid: 



SiOi 78.27 per cent., being 15.29 per cent, of whole rock. 



Al.Os 18.33 " " " 3.61 " " " " 



CaO 48 " " " .09 " 



MgO 23 " " " .04 " " " " 



Alkalies traces. 



Organic matter traces. 



97.31 19.03 



A determination of water in the dried powder gave 4 per cent, (of whole rock.) 

 Tliis is therefore a magnesian limestone, containing about 15 per cent, of silica, and but a 

 moderate quantity of oxide of iron. It would appear likely to make a good hydraulic lime. No. 

 71 might also serve that use. 



No. 71 is described by Prof. Winchell as ' light blue calciferous sandrock, from the lower 

 part of the quarry of Maxfleld and Matlier, Mankato, showing non-hydrated (un-oxidized) natural 

 condition of the deeper beds of the Shakopee formation." Prof. Dodge says of this rock:J 



Ten grammes of the powdered and dried mineral were digested with hydrochloric acid; a 

 residue was laft which weighed 1.552 gms., making 15.52 per cent, of the rock; the portion dis- 

 solved was therefore 84.48 per cent. 



A bed of clay or shale underlying the Shako|>ee limestone at the Standard Cement company's quarry, and ap- 

 parently aa*oainted with the qualities in the limestone which adapt it for the manufacture of hydraulic cement, is de- 

 scribed on pa(?e 4^4. 



tTentll annual report, p. 204. 



JSame, p. Zo3. 



