376 
PROFESSOR F. D. ADAMS AND DR. J. T. NICOLSON 
is seen in Plate 25, fig. 2. It was taken in ordinary light, and magnified 50 diameters. 
Every stage can be traced, however, from the mosaic of twinned and somewhat 
flattened grains to the areas of perfectly granulated material. Minute lines of 
granulated calcite first appear along directions of intense twisting in the mosaic, then 
these become more numerous, and finally the complete breaking down of the mosaic 
into finely granulated material, filled with twisted remnants of the calcite grains, can 
be seen. The question of time does not seem to play any important part in the 
character of the deformation. The structure of the marble deformed in 64 days 
is essentially the same in character as that which was deformed to the same 
extent in 10 minutes. In both cases the lines of cataclastic structure and the 
intervening areas composed of flattened grains are found. It seems probable, how¬ 
ever, from a study of the thin sections, that very rapid deformation tends to render 
the former structure more pronounced and more abundant, and as the granulated 
calcite is apparently the weakest portion of the mass, in this way to make the rock 
which is rapidly deformed weaker, as it is shown to be by the tests. The fact that 
the twinning and other structures above described are not developed in the cones 
proves that they are not produced by statical pressure or cubic compression, but that 
they are developed only when actual movement takes place in the mass. 
In one experiment, of which a photograph is given in Plate 23, fig. 6, under the 
pressure of the two pistons, the marble was deformed as above described, causing the 
enclosing tube to bulge in a marked manner, and the pressure being continued, the 
enclosed marble tore the wrought-iron tube apart, developing a ragged rent across the 
fibres of the iron in a vertical direction, and commenced to fall out of the rent in the 
form of a fine white powder. On removing the pressure and milling open the tube, 
the remaining marble was found to be still firm and compact, except in the vicinity of 
the rent, where it was pulverulent. 
c. Deformation of the Dry Rock at 300° C. and at 400° C. 
It was next sought to determine experimentally in what respect the second factor, 
namely, heat, would influence the result. A column of the same Carrara marble and 
of the same dimensions as those used in the former experiments was enclosed in a 
wrought-iron tube of the same construction as before. This, which is marked (A) in 
the accompanying figure (fig. 1), is surrounded by a cast-iron jacket (B), which is 
bored to receive it. The casting is so arranged that hot gases circulate in an annular 
channel (D) within it and outside of the wrought-iron cylinder (A), so that the 
marble is kept at a high temperature while the pressure is applied. The casting is as 
massive as possible so as to equalise the temperature of the interior and enable that 
of the enclosed rock to be inferred by a Callendar’s platinum resistance thermometer 
(C), which is inserted at the side of the shell in the air space (E). The hot gases are 
excluded from this space by the wall (F); and the heat flows into the cylinder and 
