15U1LDINU STONES. 175 



Limestones."] 



erected in 1820, of the Trenton limestone. It was a portion of what subse- 

 quently became Fort Snelling. 



The common-building stone of St. Paul is represented by No. 28 of the 

 general table. 



What has been said concerning the Trenton limestone as seen in St. 

 Paul, and its qualities as a building-stone, is true of it at Minneapolis, where 

 it is abundantly wrought in the numerous quarries along the river bluffs 

 below the falls, and on Nicollet island. The quarries first considerably 

 wrought were opened in 1856, and are situated a short distance below the 

 university on the east side of the river. In 1857 the first portion of the 

 state university was constructed of stone from this quarry. In 1864 the 

 quarries were opened on the west side of the river, particularly that- owned 

 by Weeks and Holscher. Mr. W. W. Eastman's quarries on Nicollet island, 

 were begun in 1865, Mr. Franklin Cook's in 1873. Several others were begun 

 in 1878, and in 1879. 



The towers of the suspension bridge over the Mississippi at Minneapolis 

 are constructed of this limestone, and most of the flouring mills of the city, 

 as well as numerous business blocks and dwelling houses. The Universalist 

 church, erected in 1873-75, and dedicated in 1876, is wholly constructed of 

 this stone. It is shown in plate GK The regular building-stone layers of 

 the Trenton in Minneapolis, are represented in the table by No. #7, taken 

 from Nicollet island. 



In the use of the Trenton limestone quarried at St. Paul and Minne- 

 apolis, regard should be had constantly to its laminated structure. The 

 beds quarried now are as they were originally deposited, and as cut for use 

 embrace in every block many layers of from one-half to two inches in thick- 

 ness. These consist of alternating clayey and calcareous portions, the latter 

 constituting the hard and enduring part of the stone. These layers are not 

 always distinct and continuous over large surfaces, but they blend or shade 

 into each other every few inches. Yet in process of time, under natural 

 weathering, they get separated so as to fall apart, the clayey parts disinte- 

 grating first and causing the calcareous structure, which sustains the whole, 

 to break up into small sheets or fragments. Hence this stone should never 

 be placed on edge, but in the same position it occupied in the quarry. It 

 should never be allowed to form projecting or exposed' parts of a building. 



