B.UILDING STOXES. 159 



Dolomites.] 



magnesia. When it is remembered that atmospheric air contains carbonic 

 acid, and that rain-water contains nitric acid, the greater destructibility ot 

 limestone as compared with magnesian limestone, not only in the weather 

 but also when subjected to artificial physical tests, is fully explained by the 

 foregoing comparisons. 



The oldest quarry in this formation, in the state of Minnesota, is that 

 of Dr. C. Carli, at Stillwater, now operated by Mr. Conkling, opened in 1847. 

 It is near the northern limits of the city, at the top of the bluff of St. Croix 

 lake. Since then several other quarries more favorably situated, have been 

 opened, and have furnished considerably more stone than that of Dr. Carli, 

 viz. those of Hersey, Staples and Hall, and of Fayette Marsh. These were 

 begun in 1854. The stone from all these quarries is of about the same 

 quality, and the stratification is very similar. There is, at least at the 

 quarries of Mr. Marsh and of Hersey, Staples and Hall, an alternation of 

 horizontal strata, from three to six feet each, of differently textured rock, 

 the whole thickness amounting to about seventy feet. One kind is coarse 

 and vesicular, of a dark color, and is used only for heavy masonry. The 

 blocks taken out are from eighteen to thirty inches thick. This is No. 18 

 of the general table. Another kind (No. 14) is useful for all work, owing to 

 its homogeneous and granular but compact texture. It yields a good sur- 

 face under the hammer, so much so that it is also employed for bases for 

 marble tombstones. It is also used for ashlers, pilasters and copings, and 

 for all common trimmings. It is in every way a valuable stone, and should 

 compete in Minneapolis and St. Paul successfully with the argillaceous 

 stone imported at considerably greater cost from Iowa (No. 40). The ridi- 

 culous infatuation for an iii/j>or/<'<l xtone is exhibited in numerous buildings in 

 Stillwater, particularly in the school-houses and churches, where can be 

 seen the blue, disintegrating shaly limestone of St. Paul used as trimmings 

 in walls made of much more durable stone quarried at Stillwater. In some 

 places the blue stone is already splitting apart in thin laminae, and will 

 wholly disintegrate long before the walls themselves show any damage 

 from the weather. Sometimes this compact and fine-grained rock is more 

 coarsely granular, or consists of little crystals of dolomite, in certain strata, 

 in which condition the quarrymen distinguish it as "sandrock." 



Some of the principal buildings that contain the Stillwater rock are 



