530 STUDIES FOR STUDENTS 



Northwestern Railway Company at Ablemans. This sample gave 

 a test of 13,431 pounds per square inch. The lowest test was 

 1658 pounds per square inch, made on a sample of Lake 

 Superior brown sandstone tested on edge. The lowest test 

 across the bed was 2502 pounds made on a sample of Dunnville 

 sandstone. The average strength of all the sandstone samples 

 tested, one half of which were on edge and the other half on the 

 bed, was 6361 pounds per square inch. The average crushing 

 strength of twenty tests of the Lake Superior brown sandstone, 

 one half of which were on edge and the other half on the bed, 

 was 4618 pounds per square inch. This is a somewhat higher 

 average crushing strength than that recorded for the Bedford 

 oolitic limestone of Indiana. 1 



The weaker the sandstone and the more uniform the grains, 

 the more perfect are the pyramids which develop. In the 

 stronger samples the pyramidal form is replaced by the conical. 

 In the samples of moderate strength almost perfect pyramids 

 form on both the upper and lower sides, as shown in the accom- 

 panying illustration, Plate IV, Figs. 1 and 4. 



In performing these tests my attention was called to the fact 

 that the crushing strength on edge of the weakest samples 

 was considerably less than that on the bed, while in the stronger 

 rocks the difference was much less. The compressive strength 

 of several different limestones was higher when the pressure was 

 applied along the bed than when applied across it. The Berlin 

 rhyolite, which is the strongest stone tested, gave the highest 

 strength test when the pressure was applied in the direction of 

 easiest parting. These results indicate that there are exceptions 

 to the general rule that a stone will withstand the greatest pres- 

 sure when applied normal to the bed. Apparently the rule 

 applies only to stone which has a low compressive strength. 

 When the compressive strength is very high the opposite result 

 is fully as likely to occur and may even prove the rule. 



The manner in which the cubes of stone break indicates to a 



greater or less extent the strength of the stone. Crushing a 



1 Twenty-first Annual Report of the Indiana Department of Geology and Natural 

 Resources, p. 317. 



