400 PROCEEDINGS OF THE ALBANY MEETING 



which thus helped to maintain the strength of the rock. No signs of such deposi- 

 tion, however, were visible. 



By studying the marble deformed at a temperature of 300 degrees centigrade, or 

 better at 400 degrees centigrade, it will l)e seen that structures induced in it by the 

 movements, and the nature of the motion, ai"e precisely the same as those observed 

 in metals when they are deformed by impact or by compression. In a recent 

 paper by Messrs Ewing and Rosenhain, "Experiments in Micro-metallurgy: 

 Effects of Strain," which appeared in the Proceedings of the Royal Society of Lon- 

 don, three photographs of the same surface of soft iron, showing the results of 

 progressive deformation under pressure, are shown, which photographs could not 

 be distinguished from those of thin-sections of the marble described in the present 

 paper, at corresponding stages of deformation. In botii cases the movements are 

 caused by tiie constituent crystalHne individuals sliding upon their gliding planes 

 or by polysynthetic twinning. In both cases the motion is facilitated by the appli- 

 cation of heat. The agreement between the two is so close that the term " flow " 

 is just as correctly applied to the movement of the marble in compression under 

 the conditions described as it is to the movement which takes place in gold when 

 a button of that metal is squeezed flat in a vise, or in iron when a billet is passed 

 between rolls. 



In order to ascertain whether the structures exhibited 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 develo})ed 

 in the Carrara marble. In six other cases the structures 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 differential pressures exceeding the 

 elastic limit of the rock and under the conditions described in this paper, perma- 

 nent deformation can be produced. 



2. This deformation, when carried out at oi'dinary temperatures, is due in part 

 to a cataclastic structure and in part to twinning and gliding movements in the 

 individual crystals comprising the rock. 



3. Both of these structures are seen in contorted limestones and marbles in 

 nature. 



4. When the deformation is carried out at 300 degrees centigrade, or better at 

 400 degrees centigrade, the cataclastic structure is not developed, and the whole 

 movement is due to changes in the shape of the component calcite crystals by 

 twinning and gliding. 



5. This latter movement is identical with that produced in metals by squeezing 

 or hammering, a movement which in metals, as a general rule, as in marble, is 

 facilitated by increase of temperature. 



6. There is therefore a flow of marble just as there is a flow of metals, under 

 suitable conditions of pressure. 



7. The movement is also identical with that seen in glacial ice, although in the 

 latter case the movement may not be entirely of this character. 



