Adams c& Coker^The Flow of Marble. ±*IT 



surface of this cake no reticulating (Luder's) lines such as 

 those observed when marble is deformed in Kick's experiment 

 are seen. 



A series of thin sections of the deformed marble was then 

 prepared. "When examined under the microscope these sec- 

 tions show that the marble has had developed in it a most 

 striking and beautiful foliated structure due to the arrange- 

 ment of individuals of calcite, each of which has been "flattened 

 out so that in a section passing vertically through the deformed 

 column it presents the appearance of a ribbon drawn to a 

 point at either end and from eight to ten times as long as it 

 is wide. These elongated calcite individuals are perfectly 

 moulded upon one another, coming together along sharp and 

 gently sinuous lines. A microphotograph of this deformed 

 rock, together with one of the original marble, is shown in 

 Plate III. While many of them possess a very fine polysyn- 

 thetic twinning, causing them to maintain a generally uniform 

 illumination as they are revolved between crossed nicols, the 

 movement has evidently been chiefly of the nature of a trans- 

 lation or slipping on gliding: planes without the development 

 of pronounced twinning, so that the elasticity axes of the vari 

 ous individuals lie nearly parallel to one another, and the whole 

 rock section thus becomes light and dark four times during a 

 revolution between crossed nicols, the periods of extinction 

 being reached when the longer axes of the crystals (i. e., the 

 foliation of the rock) coincide with the vibration planes of the 

 nicols. In sections parallel to the foliation, the flattened indi- 

 viduals are seen to have a rudely polygonal form, often pre- 

 senting somewhat rhombic outlines, some showing strain 

 shadows which in many cases can be seen to result from a poly- 

 synthetic twinning of almost ultra-microscopic minuteness. 

 This is of especial interest, as it is precisely this movement of 

 individual lamellae of measurable width over one another that 

 gives rise to the phenomenon of the u flow " of metals. Calcite, 

 however, is apparently much more prone to twin during this 

 deformation than metals are, although the greater difficulty of 

 recognizing twinning in metals — the latter being opaque — may 

 have led to the frequency of this phenomenon in their case 

 being underestimated. 



The marble shows no trace of granulation and the movement 

 set up in it is an example of perfect plastic flow. 



The rock has a distinct foliated structure and the plane of 

 foliation is transverse to the vertical axis of the deformed col- 

 umn, that is to say. at right angles to the direction of pressure 

 in that part of the column between the piston faces, but imme- 

 diately about the sides of the highly deformed and flattened 

 column the foliation bends up until it runs approximately par- 



