148 THE GEOLOGY OF MINNESOTA. 



[Crystalline rocks. 



colors in polarized light is nearly as brilliant as that of the labradorite. Plate A, fig. 6 is so drawn 

 as to show a fibrous grain of augite, surrounded by labradorite containing scattered impurities. 

 In some parts of this rock the magnetite, which is titaniferons, is very rare, and then it becomes 

 the rock No. 8, and in some places it is so abundant as to compose the greater part of the mass, 

 making an iron ore.* Figures 1 and 2, plate B, represent a section of the labradorite of Beaver Bay 

 (No. 8) magnified forty diameters, the former in common light and the latter between crossed 

 Nicols. 



The "granites" of Minnesota are adaptable to a wide range of architect- 

 ure. That which is most used from St. Cloud (No. 1), is of a neutral gray 

 color, of rather fine, inconspicuously granular texture, and has a resisting 

 strength of over twenty-five thousand pounds per square inch. It resists 

 fire and the sudden cooling produced by cold water thrown upon it, 

 better than the more quartzose, and more coarsely granular rocks quar- 

 ried at East St. Cloud and Watab. The other varieties, however, are more 

 showy in construction, on account of their lighter color as well as their 

 more close crystalline texture. Some of them will take and preserve a bet- 

 ter polish, particularly Nos. 6 and 7, and are to be preferred for that reason 

 for fine work, such as monuments or tablets, and for all inside trimmings. 

 The syenite from Beaver Bay has a uniformly brownish red color and fine 

 grain, and when polished is very beautiful. 



These crystalline rocks have been used in some of the principal build- 

 ings in St. Paul and Minneapolis for trimmings, and have been sent for the 

 same purpose to several other cities, particularly to Milwaukee, Chicago 

 and DesMoines. At Sauk Rapids the fine-grained gray syenite (No. 1) is 

 made into monuments. Stone from the Sauk Rapids quarries was used in 

 the trimmings of the state capitol at Des Moines, and constitutes the entire 

 front wall of the block of Nicols and Dean, at St. Paul. It is that used for 

 paving at Minneapolis and St. Paul. The trimmings of the U. S. custom 

 house and post office at St. Paul were taken from the East St. Cloud 

 quarries, and embrace all the principal varieties there found, i. e. Nos. T, 6 

 and 7. Much of the stone put into the bridge over the Missouri river at 

 Bismarck for the Northern Pacific railroad, came from East St. Cloud, but 

 at a point further southeast than the quarries of Breen & Young, and con- 

 sists of another variety (No. 9) of syenite. This rock seems to have stood 

 the physical tests that have been made by the survey, on Minnesota 

 building stones, less successfully than the other crystalline rocks. This, 



Tenth annunl report, p. 80 Rock sample No. 695. 



