16 



TWELFTH ANNUAL REPORT. 



the strength on edge is reported greater than on bed) I have chosea 

 the strength on bed^ when known. I have avoided every possible 

 error that might be made in favor of the Minnesota granites, and 

 allowed several points that count in favor of the New England 

 granites. 



Table 



showing the compressive strength of Neiv England granites in 2-inch 

 cubes, as reported by Gen. Gillmore (Report of the Chief of En- 

 gineers, 1875, Part II). In unpolished cubes, on wooden cushion- 

 blocks. 







Position. 



Strength in poinds 





of sample, per square 



Blue. 



Staten I., New York. 



Fox Island, Me. 



Dix Island, Me. 



c^uincy, Mass. 



(Juincy, Mass. 



North river, N. Y. 



Cape Ann, Mass. 



Mystic river, Conn. 



Stony creek, Conn. 



Fall River, Mass. 



Keene, N. H. 



Keene, N. H. 



Millstone Ft , Conn. 



Greenwich, Conn. 



New London, Conn. 



New London, Conn. 



Vinal Haven, Me. 



VInal Haven, Me. 



Westerly, R. L 



Westerly, R. I. 



On bed 



89,250 

 59,500 

 60,000 

 71.000 

 59,000 

 53,700 

 50.750 

 72,500 

 60,000 

 63,750 

 41,000 

 51, .500 

 64,750 

 45,200 

 50,000 

 56,700 

 52,600 

 ^,000 

 58,750 

 59,750 



22,315 

 14,875 

 15,000 

 17,750 







Dark. 





Light. 





14,750 



Flagging. 





13,425 





On bed 

 On bed 

 On bed 

 On bed 

 On bed 

 On bed 



14,937 

 18.125 

 15,000 

 15,937 

 10,2.'^) 

 12,875 

 16,187 

 11,300 

 12,500 



Porrpi'srock. 



Gray. 



Gray. 

 Bluish gray. 

 Bluish gray. 



Nian tic river. . 





Niantic river.. 



On edge 



14,175 

 13,150 







16.750 





On bed 

 On edge 



14,687 





14,937 









Average of 20 granites 





59,785 



14.946 



We find here that the 



Average strength of 20 Netv England granites, unpolished, crushed 

 betiveen wooden cushions in 2-inch cubes, is, in pounds, per 2-inch 

 cube, 59,785; per square inch, 14,946, 



This shows that the average strength of the Minnesota granites 

 is fifty-six per cent of the strength of the New England granites 

 greater than that of the New England granites. 



This anomalous result was so striking that I called general Gill- 

 more's attention to it. The strength of the Minnesota 2-inch 

 cubes was so great that it exceeded the highest registration of the 

 gauge in use, and the samples were not reported ai first, but were 

 retained for crushing on a more powerful machine at Boston. It 

 occurred to me that possibly there had been a gradual deterioration 

 in the machine, or in the gauge, so that the registration was uni- 



