OX AX EXPERIMENTAL INVESTIGATION IXTO THE FLOW OF MARBLE. 385 
the results of the test just described show that the marble after deformation is not 
weaker, hut actually somewhat stronger than the original rock. 
A large number of thin sections of the deformed rock (some radial and some trans¬ 
verse) were prepared and examined. The rock shows the continuous mosaic before 
referred to with the exception of a little turbid line or band in each section, starting 
from the periphery of the top of the cylinder, and curving down toward the middle, 
following approximately the curve of the surface of one of the cones. Under the 
microscope this is seen to owe its appearance to the presence of a number of fine and 
very narrow reticulating lines, which appear to be lines of motion along which there 
has been a very minute granulation of the marble. Between these, and elsewhere 
throughout the column, there are no signs of granulation or cataclastic structure. 
This granulated material is so trivial in amount, that the deformation may he said to 
be due exclusively to movements on the gliding planes of the calcite, accompanied by 
polysynthetic twinning. It is thus identical in character with that seen in the case 
of the marble when deformed while dry, either at 300° C. or 400° C. The calcite 
individuals in the original rock are approximately equidimensional (none are more 
than twice as long in one direction as in the other), but in the deformed rock a very 
distinct foliation is often seen in the thin sections, owing to the flattening of the 
calcite grains, many individuals being three or even four times as long as they are 
wide. Some few of these flattened grains show strain shadows but no twinning, 
while the grains in their immediate vicinity show well-defined twinning, giving rise 
to the fibrous appearance before described. In some cases a grain will show strain 
shadows at one end, which will pass into a very narrow polysynthetic twinning at the 
other. The twin lamellse in many grains are so narrow that even when magnified 
1050 diameters, they are not very clearly resolved. The individual lamellae in several 
sets which were measured, were found to have an average width of between ‘0005 
and ‘0006 of a millim., and some were even narrower. 
Where the iron stain has penetrated into the substance of the rock, it appears 
under the microscope as little lines of ferruginous material between the calcite grains, 
which latter are twinned and flattened in every way like those above described. 
There are no signs of solution and redeposition of calcium carbonate even in this iron- 
stained portion of the rock. 
The presence of water, therefore, did not influence the character of the deformation. 
It is just possible, however, that there may have been a deposition of infinitesimal 
amounts of calcium carbonate along very minute cracks or fissures, thus contributing 
to maintain the strength of the rock, bio signs of such deposition, however, are 
visible. 
9 
3 D 
VOL. CXCV. —A. 
