OX AX EXPERIMENTAL INVESTIGATION IXTO THE FLOW OF MARBLE. 379 
made, it is clear that the deformed marble, if not quite as strong, is at least very 
nearly as strong as the original rock. Twenty thin sections were cut from a portion 
of the other half-column and examined under the microscope. The sections show 
that the deformed rock possesses a more or less distinct foliation except at the ends 
of the column, where practically no motion had taken place. Here scarcely any 
trace of foliation is visible. Cataclastic structure is absent, but almost every grain 
shows an exceedingly fine fibrous structure. When examined under a high power 
this fibrous structure resolves itself into an extremely narrow polysynthetic twinning 
—the whole grain consisting of slightly sinuous twin lamellae, extinguishing in alter¬ 
nate sets. Each individual is usually twinned throughout, the lamellae passing from 
end to end, although a single lamella often varies somewhat in width from place to 
place. The calcite grains which in the original rock are practically equidimensional, 
are now often distinctly flattened (fig. 2), some of them being three or even four times 
as long as they are wide. Some grains can be seen to have been bent around others 
adjacent to them, the twin lamellae and the extinction curving with the twisted grain 
(fig. 3). In other twisted individuals the twin lamellae only extend in to a certain 
distance from the margin of the grain, leaving a clear untwinned portion in the centre 
(fig. 4) ; and other crystals again show not only the fibrous structure due to twinning 
in one direction, but broader lamellae crossing this obliquely. As the twinning in all 
cases is probably parallel to — 111 — this is due to the appearance of a set of twin 
lines parallel to a second face of the rhombohedron (fig. 5). 
Fig. 4. 
Fig. 5. 
Cleavage is not developed by the crushing, for it is not seen in the majority of 
grains, even where they are most deformed. The proportion of grains which show it 
is no greater in the deformed than in the original limestone. What cleavage is 
visible was probably developed during the grinding of the section, as it is seen in 
3 C 2 
