III. 



THE COMPARATIVE STRENGTH OF MINNESOTA 

 AND NEW ENGLAND GRANITES. ^ 



By N. H. WINCHELL. 



Having had occasion recently to investigate the qualities of some 

 of the building-stones of the state of Minnesota, I found it neces- 

 sary to subject them to the usual test of crushing, in the form of 

 two-inch cubes, to learn their strength under pressure. 



Samples were obtained and dressed to the required size by Mr. 

 William Keating, at the marble shops of Messrs. Sullivan and 

 Farnham, in this city. About one hundred of such cubes were 

 formed, embracing sandstones, limestones, granites and trap rocks. 

 It is intended in this paper to show the remarkable, and unexpected 

 strength exhibited by the crystalline rocks of the state, and espe- 

 cially their superiority in that respect over the granites of New 

 England. 



The samples as prepared were carefully chosen to avoid flaws and 

 imperfections due to weathering. They were dressed by hand with 

 hammer and chisel on all six sides, so as to measure two inches on 

 all their edges, the sides all being exact squares. They were sent 

 to Gen. Gillmore, at Fort Wadsworth, Staten Island, where they 

 ■were subjected to the test for crushing-strength in the same manner 

 as many other granites that have been tested and reported by him 

 in his reports to the chief of engineers, fro.u other portions of the 

 United States and particularly from New England. The tests were 

 applied by Mr. James Cocroft, under the direction of Gen. Q. A. 



1 Read at the Minneapolis meeting of the American Association for the Advancement Of 

 Science. August, 1883. 



