FRICTION AND LIMITING STRENGTH OF ROCKS 653 



PLATE II 



zz longitudinal 

 pressure 

 thousand 

 lbs. per 

 sq. in. 



Belgian Black Marble 

 Dolomite 



Carrara Marble 

 Sandstone 



xx lateral pressure 

 thousand lbs. 

 per sq. in. 



Relative Plasticities of Various Rock Specimens 

 Nickel-steel jackets of o . 33 cm. wall 



