380 
PROFESSOR F. D. ADAMS AND DR. J. T. NICOLSON 
places in sections of all marbles. There has been no breaking—the rock has not been 
crushed in the ordinary sense of the term. The movement has been brought about 
partly by twinning but chiefly by a deformation of the grains due to a slipping on 
their gliding planes. The structure is essentially that presented by those portions of 
the marble lying between the lines of granulated calcite in the case of the marble 
deformed at the ordinary temperature. In the accompanying plates, microphoto¬ 
graphs of the marble before and after deformation at 300° C. are shown. 
Plate 24, fig. 1, shows the appearance of a thin section of the original Carrara 
marble in ordinary light, magnified 50 diameters. The individuals are approximately 
equidimensional, and only three or four show twinning. 
Plate 24, fig. 2, is the marble after having been slowly deformed at a temperature 
of 300° C., photographed between crossed nicols in polarised light and magnified 
50 diameters. The individual grains can be seen to be distinctly flattened in a 
horizontal direction, giving a certain foliation to the rock. The fibrous appearance 
above referred to, as due to polysynthetic twinning, is also seen. 
Plate 24, fig. 4, is a microphotograph of a few grains of calcite, the thinnest edge of 
another section of the same, taken between crossed nicols in polarised light and 
magnified 150 diameters. The polysynthetic twinning is well seen. Two sets of 
lamellae cross and two of the bands represented in fig. 5 of the text are seen on the 
left. The lamellae curve somewhat and vary more or less in width from place to 
place. 
In the case of ice crystals a rise in temperature develops a greater ease of move¬ 
ment along their gliding planes, and this experiment seemed to show that the same is 
true of calcite. The individual grains are more plastic and accommodate themselves 
to the deforming forces by flowing around each other more readily rather than by 
breaking. The rock is therefore much stronger than when deformed at the ordinary 
temperature, the lines of cataclastic structure being apparently lines of weakness. 
As, however, the deformation in this experiment was carried on with extreme slowness, 
it was impossible to determine in how far this latter factor had influenced the result. 
Another trial was accordingly made in which the deformation was carried out quickly 
and at the same time at a much higher temperature. The amount of deformation 
induced in the marble was nearly the same as in the last case. The height of the 
column before compression was I '552 inch, and after compression 1 '352 inch ; that is 
to say, the column was shortened by 12'9 per cent. The time occupied in the 
deformation, however, was only 8-|- hours, and the rock was maintained at a tem¬ 
perature of about 400° C. ; the extremes of variation of the temperature during the 
experiment being 380° C. to 415° C. Tbe temperature measurements were made by 
means of a special modification of the Le Chatelier pyrometer, calibrated by H. M. 
Tory, M.A., of McGill University. On slitting the tube in the usual manner and 
inserting the wedge to split the marble, the latter was found to offer more resistance 
than in any of the former experiments, and was finally pulled out of the separated 
