An Experimental Investigation into the Flow of Marble. 229 



cerning the conditions which are necessary in order that the move- 

 ments in question may take place. 



It is generally agreed that three chief factors contribute to bringing 

 about the conditions to which rocks are subjected in the deeper parts 

 of the earth's crust, where folding with concomitant flowing is most 

 marked. These are : 



1. Great pressure. 



2. High temperature. 



3. Percolating waters. 



With regard to the first factor, it must be noted that mere cubic 

 compression does not produce movements of the nature of flowing, 

 although it may produce molecular rearrangement in the rock. A 

 differential pressure is necessary to give movement to the mass. As 

 Heim has pointed out, there is reason to believe that " Umformung 

 ohne Bruch " takes place when a rock is subjected to a pressure which, 

 while greater in some directions than in others, in every direction 

 exceeds the elastic limit of the rock in question. Whether all these 

 factors, or only certain of them, are actually necessary for the produc- 

 tion of rock deformation is a question which also requires to be deter- 

 mined by experiment, for by experiment the action of each can be 

 studied separately, as well as in combination with the others. 



In the paper of which this is an abstract, a first contribution to such 

 a study is presented, pure Carrara marble being the rock selected for 

 gtudy. The investigation is now being extended to various other 

 limestones, as well as to granites and other rocks. 



In order to submit the marble to a differential pressure, under the 

 conditions above outlined, it was sought to enclose the rock in some 

 metal having a higher elastic limit than marble, and at the same time 

 possessing considerable ductility. After a long series of experiments, 

 heavy wrought-iron tubes of special construction were adopted. These 

 were made, following the plan adopted in the construction of ordnance, 

 by rolling thin strips of Low Moor iron around a bar of soft iron, 

 and welding the strips successively to the bar, as they were rolled 

 around it. The core of soft iron composing the bar was then bored out, 

 leaving a tube of Low Moor iron, the sides being about ^ inch in thick- 

 ness, and so constructed that the fibres of the iron ran around the tube 

 instead of being parallel to its length. These were found to answer 

 the requirements admirably. 



The following procedure was then adopted. Columns of the marble, 

 an inch or in some cases 0'8 inch in diameter and about 1'5 inch in 

 length, were accurately turned and polished. The tube was then very 

 accurately fitted around the marble. This was accomplished by 

 giving a very slight taper to both the column and the interior of 

 the tube, and so arranging it that the marble would only pass half 



