The Fioio of Marble. 435 



sive deformation under pressure, are shown, wliicli 

 piLOtographs could not be distinguished from those of 

 thin sections of the marble described in the present 

 paper, at corresponding stages of deformation. In 

 both cases, the movements are caused by the constitu- 

 ent crystalline individuals sliding upon their gliding- 

 planes or by polysynthetic twinning. In both cases 

 the motion is facilitated by the application of heat. 

 The agreement between the two is so close that the 

 term '"' flow " is just as correctly applied to the move- 

 ment of the marble in compression under the condi- 

 tions described, as it is to the movement which takes 

 place in gold when a button of that metal is squeezed 

 flat in a vice, or in iron when a billet is passed 

 between rolls. 



In order to ascertain whether the structures exhib- 

 ited by the deformed marble were those possessed by 

 the limestones and marbles of contorted districts of 

 the earth's crust, a series of forty-two specimens of 

 limestones and marbles from such districts in various 

 parts of the world were selected and carefully studied. 

 Of these, sixteen were found to exhibit the structures 

 seen in the artificially-deformed marble. In these 

 cases the movements had been identical with those 

 developed in the Carrara marble. In six other cases 

 the structure bore certain analogies to those in the 

 deformed rock but were of doubtful origin, while in 

 the remaining twenty the structure was different. 



The following is a summary of the results arrived 

 at : — 



1. By submitting limestone or marble to difl'erential 

 pressures exceeding the elastic limit of the rock and 

 under the conditions described in this paper, perman- 

 ent deformation can be produced. 



