324 CALIFORNIA ACADEMY OF SCIENCES. 



however, bending seems to have about reached its limit, 

 as a thread-like crack about two inches long and 24 >^ 

 inches from the head of the slab can be detected on the 

 side toward the observer. 



As shown, other slabs cover other parts of the group 

 of graves and of these, two are bent more or less but not 

 as much as the one described. 



If 160 pounds be taken as the weight of a cubic foot 

 of marble (a fair average), the weight of a prism an inch 

 square and the thickness of the slab will be almost .07 of 

 a pound. We may therefore consider .07 of a pound to 

 the square inch as the bending pressure. 



Considering the curve of the slab an arc of a circle, a 

 continuous piece of limestone having the same curve 

 would form a closed circle with a radius of 37 feet. 



In summary, a slab of marble ^,{ of an inch thick under 

 a stress of .07 of a pound per square inch has in 10 years 

 become flexed one forty-sixth of its length. 



