Adams <& Coker — The Flow of Marble. 481 



The thickness of the tube walls was accordingly increased to 

 l cm , that is to say, the thickness was doubled. It was found, 

 however, that with a wall of this thickness it was impossible 

 to confine the bulging of the marble to the thinner portion of 

 the tube and thus secure a symmetrical barrel-shaped mass of 

 deformed rock. The pressure required for this deformation 

 was 387,000 lbs. to the square inch (273,000 kilos, per square 

 cm.), and was so great that when subjected to it the marble 

 forced its way up between the pistons and the walls of the tube, 

 and the thin, wedge-shaped ridges so produced broke away and 

 crumbled to powder as the steel tube was being turned off in 

 a lathe. 



Attempts were then made, by increasing the length of the 

 marble column and altering the dimensions of the enclosing tube, 

 to prevent the rock forcing its way up between the pistons and 

 the thicker ends of the tube. These attempts, however, were 

 unsuccessful, and it was evident from them that the result 

 could c Aj be accomplished by greatly increasing the thickness 

 of that portion of the walls which enclosed the pistons, which 

 would in its turn necessitate the employment of a much higher 

 pressure to deform the rock, and this would result in the de- 

 struction of the pistons themselves. In the case of these exper- 

 iments under very high pressure, furthermore, it was found 

 that the deformed marble could not be obtained as a solid 

 mass, for so soon as the last thin remnant of the steel tube 

 which was left by the lathe was filed through, the marble 

 developed cracks running across the column at right angles to 

 its vertical axis. In some cases the deformed limestone at once 

 broke in two along one of these cracks. In other cases it was 

 obtained in what was apparently a solid mass, but upon stand- 

 ing a few minutes little transverse cracks, running partially or 

 completely across the specimen, made their appearance. This 

 phenomenon is apparently due to the expansion of the mass 

 upon its relief from the tremendous pressure consequent upon 

 the removal of the enclosing tube and is not confined to marble 

 deformed under very high pressures, but is met with, as will 

 be mentioned, in the case of the various impure limestones and 

 dolomites whose deformation will be described later. 



It was, therefore, found to be impossible to test the strength 

 of the marble when deformed at these highest pressures owing 

 to the fact that these transverse cracks invariably developed, 

 thus destroying the continuity of the rock. 



(d) Influence of rest and of heat on the strength of the deformed 

 marble. 



It has long been known that iron which has been over- 

 strained, that is to say strained beyond its elastic limit, pos- 



Am. Jour. Sci.— Fourth Series, Vol. XXIX, No. 174.— June, 1910. 

 32 



