ON AN EXPERIMENTAL INVESTIGATION INTO THE FLOW OF MARBLE. 375 
the deformed rock possibly influenced in their position to some extent by the cones 
produced in deforming the rock, do not result from them, since, as above mentioned, 
they are always observed in the case of the original marble as well. 
Thin sections of the deformed column passing vertically through the unaltered cone 
and the deformed portion of the rock were readily made, and when examined under 
the microscope clearly showed the nature of the movement which had taken place. 
The deformed portion of the rock can be distinguished at once by its turbid appear¬ 
ance, differing in a marked manner from the clear transparent mosaic of the unaltered 
cone. In those cases where the deformation has been rapid, as in Experiment P of 
the above list, an anastomosing and complicated rneshwork of curved and branching 
lines, which are especially turbid in appearance, are seen running through the rock. 
These, when magnified 500 diameters, are resolved into strings or bands of very small 
calcite granules. They mark lines along which shearing has taken place. The calcite 
individuals along these lines have broken down, and the fragments so produced have 
moved over and past one another and remained as a compact mass after the movement 
ceased. In these lines of granulated material are enclosed great numbers of irregular 
fragments and shreds of calcite crystals, bent and twisted, which have been carried 
along in the moving granulated mass as the shearing progressed. The structure is 
therefore cataclastic, and is identical with that seen in the felspars and many 
gneisses. A microphotograph of a thin section of the deformed marble showing this 
structure is r.een in Plate 25, fig. 1. It is taken in ordinary light, and magnified 
70 diameters. The original column in this case had a diameter of 1'067 inch, which 
was increased by the pressure to 1'356 inch along the line £>f greatest bulging. The 
deformation was carried out in 7 hours. The dark areas are the granulated portions 
of the rock in wdiich the fragments of calcite individuals, often distinctly twinned, 
are seen to be embedded. 
Between these lines of granulated material the marble shows movements of 
another sort. Most of the calcite individuals in these portions can be seen to have 
been squeezed against one another, and in many cases a distinct flattening of the 
grains has resulted with marked strain shadows, indicating that they have been bent 
or twisted. They show, moreover, a finely fibrous structure in most cases, which, 
when highly magnified, is seen to be due to an extremely minute polysynthetic 
twinning. The chalky aspect of the deformed rock is chiefly due to the destruction 
by this repeated twinning of the continuity of the cleveage surfaces of the calcite 
individuals, thus making the reflecting surfaces much smaller. 
By this twinning the calcite individuals are enabled under the pressure to alter 
their shape somewdiat, while the flattening of the grains is evidently due to 
movements along the gliding planes of the crystals. This, however, will be referred 
to again. 
In these parts, therefore, the rock presents a continuous mosaic of somewhat 
flattened grains. A microphotograph of a portion of the rock showing this structure 
