156 THE GEOLOGY OF MINNESOTA. 



[ Dolomites. 



to atmospheric influences ; indeed it has not been in use long enough yet in 

 the state to show any change whatever by lapse of time, although it is in 

 some of the oldest buildings of the state. The homogeneity of its texture 

 and composition, and the regularity and thickness of its bedding, are quali- 

 ties that enable it to supply slabs and blocks of any desired dimensions. At 

 Frontenac it is cut into ornamental forms with comparative ease, and the 

 same kind of beds as those at Frontenac are found throughout the south- 

 eastern part of Goodhue county, and the northern portion of Wabasha. Its 

 resistance to pressure, amounting sometimes to 25,000 pounds per square 

 inch, is more than that of most granites,* and is sufficient to warrant its use 

 in all structures, while for door moldings and caps, for sills and water-tables, 

 and for all trimmings to brick structures it is unsurpassed. 



As a material for building, dolomites and dolomitic limestones rank 

 very high. Numerous remains of Roman architecture in England, and par- 

 ticularly at York, the seat of the commercial and military power of the 

 Roman empire in Britain, have been found executed in dolomitic limestone, 

 and many of them are in a better state of preservation than the generality 

 of structures of later date.f Conisburgh castle, as old as the time of the 

 Normans, situated between Doncaster and Rotherdam, is built ot a coarse- 

 grained, semi-crystalline and partially oolitic magnesian limestone, and 

 some of the blocks still show the marks of the chisel. The old Southwell 

 church is constructed of magnesian limestone from Bolsover Moor. The 

 new houses of parliament at Westminster are constructed of dolomite or 

 dolomitic limestone, quarried at Norfal near North Anston, England. This 

 stone was chosen after an exhaustive search throughout the British islands 

 by a government commission, as the most suitable, all things considered, for 

 the important structures that were contemplated, notwithstanding the gra- 

 tuitous offer of granites from Scotland. This stone from North Anston is 

 nearly a pure dolomite, containing from forty-four to forty-five per cent, of 

 carbonate of magnesia, and about two per cent, of silica, iron and alumina. 

 The report of the commission, consisting of Sir Henry T. De la Beche and 

 Dr. William Smith, geologists, Charles Barry, architect, and Charles H. 



*Of ninety-nine tests of granites, reported by general Gillmore in the report of the chief of engineers, 1875, part 

 II. p. 846, not one reached 26,000 pounds per square inch. 



tlathology, or observations on stone used for building. C. H. Smith. 



