THE GEOLOGY OF MINNESOTA. 



[Sand. Calcareous tufa. 



form firmness. There are, however, some portions of the county where it 

 is'much more difficult to obtain a sand suitable for common mortar. In 

 the western part of the county a white sanu, or one nearly white, is ob- 

 Mned from; deposits. referable to the Lower Cretaceous. These have been 

 mentioned under the head of Cretaceous. They are found on the land of 

 QoddBMBpieeSffiui sec. 8, Bloomfield; on sec. 17, Spring Valley; on Andrew 

 M^Nee's land, N. W. \ sec, 22, Bloomfield; and on J. M. Eexford's, N. E. J 

 sec. 36. Mr. Temple delivers sand at Spring Valley for $1.75 per load of 

 two tons. One team can haul five such loads per day, but generally hauls 

 three; From three fto five hundred dollars worth are taken from Mr. Tem- 

 ple's sand pit annually. Besides these sources for mortar sand, the Jordan 

 sandstone which is often as incoherent as the St. Peter, can be used to ad- 

 vantage, though it is rather more apt to be cemented by iron. There can 

 be no question that the compact and impervious nature of the green shales 

 of -the "Hudson River have preserved the incoherency of the St. Peter, by 

 preventing the downward percolation of ferriferous and calcareous waters 

 which certainly would have left their impurities in the form of cement 

 among? ifc$< beautiful white grains. 



I'l^iTke proximity and cheapness of lime and sand have suggested the 

 building of 'houses by mixing these substances in the form of a concrete. 

 Several such are found at Fillmore, also in Jordan and at Rushford; but 

 this method ; is not general. The material is cast in the form of large brick, 

 having the 'color of common brown mortar, and these blocks are laid up 

 much likei common brick walls. Patent presses are used to make the con- 

 crete blocks, iri 



ni -Galcarebus tufa. At Chatfield there is considerable travertine in the 

 tohiff& on the north side of the creek, and on the limestone layers, in the 

 seams, '';It has become crystalline in some cases, and lies in successive lam- 

 inations that have a color like brown sugar, and resembles the lamellar 

 calcite of Houston county. 



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