STATE GEOLOGIST. 17 



formly too high, and this impression was strengthened by compar- 

 ing the results with the results reported in 1875, for some other 

 stones. One of the limestones reported in 1875 was from the same 

 place (Lemont, 111.) as one of those I had included in my series, 

 the same being used largely in this city. While at that time the 

 strength of this stone did not reach beyond 14.000 pounds per 

 square inch, the samples I had sent was not crushed because it ex- 

 ceeded 100,000 pounds, the limit of the gauge. Again, one of the 

 granites sent in my series, had been reported in 1875. I refer to 

 that from St. Cloud. The gabbro from Duluth had also been re- 

 ported. Neither of these then reached beyond 19.000 pounds per 

 square inch, but now one is reported at about 26,000 pounds, and 

 the other about 27.000. 



I called Gen. Gillmore's attention to these discrepances in order 

 that if any error had been committed it might be detected by a re- 

 testing of his gauge, and the proper correction applied before the 

 results were published. Subsequently Mr. Cocroft wrote me that 

 he had the hydrostatic press taken apart and refitted, and the old 

 gauge tested by its maker, who formed a variation of only 200 

 pounds in 100,000 pounds. On reporting this to general Gillmore, 

 Mr. Cocroft was authorized to hare a new gauge made, which 

 should register 175.000 pounds. This new register was used in 

 testing the refractory 2-inch cubes from Minnesota; hence their 

 actual strength is as certainly ascertained as is possible with the 

 apparatus employed. 



Now, in discussing this curious anomaly, in order to reach an 

 explanation of it, we are driven to one of three conclusions. 



1. Either the cubes used were too large, or, 



2. The methods are defective, or, 



3. Mmnesota granites are actually stronger than those of New 

 England. 



(1) Were the cubes too large? I show here several surplus 

 cubes of the same size and style, made at the same time and by the 

 same man, with the same instruments. These are exactly two 

 inches on a side, measured with any ordinary standard. It is 

 evident the great excess of strength shown by the Minnesota cubes 

 cannot be due to their greater size, since the cubes would require 

 to have been very noticeably and remarkable greater than two 

 inches, and they would have been condemned. 



(2). Are the methods defective? It would be sufficient, perhaps, 

 to answer that the tests were made with the exactness and well- 

 known integrity of the United States Engineers, under the direc- 

 S 



