458 PROCEEDINGS OF THE ALBANY MEETING 



is necessary to spread the latter in a vise in order to set tliein free. The deformed 

 marble, while firm and compact, differs in appearance from the original rock in 

 possessing a dead white color, somewhat like chalk, the glistening cleavage surfaces 

 of the calcite being no longer visible. The difference is well brought out in cer- 

 tain cases, owing to the fact that a certain portion of the original marble often re- 

 mains unaltered and unaffected by the pressure. This when present has the form 

 of two blunt cones of obtuse angle whose bases are the original ends of the columns 

 resting against the faces of the steel plugs, while the apices extend into the mass 

 of the deformed marble and point toward one another. These cones, or rather 

 parabolas of rotation, are developed, as is well known, in all cases when cubes of 

 rock, Portland cement, or cast iron are crushed in a testing machine in the ordinary 

 manner. In the present experiments they seldom form any large portion of the 

 whole mass. 



In order to test the strength of the deformed rock, three of the half columns 

 from different experiments, obtained as above described, were selected and tested 

 in compression. The first of these, which had been deformed very slowly, the 

 experiment extending over 64 days, crushed under a load of 5,350 pounds per 

 square inch ; the se<'ond, which had been deformed in U hours, crushed under a 

 load of 4,000 pounds per square inch; while the third, which had been quickly 

 deformed, the experiment occupying only 10 minutes, crushed under a load of 

 2,77fi pounds per square inch. As mentioned above, the original marble, in columns 

 of the dimensions ])0ssessed by these before deformation, was found to have a 

 crushing weight of between 11,430 and 12,026 pounds per square inch. These 

 figures show that, making all due allowance for the difference in shape of the 

 specimens tested, the marble after deformation, while in some cases still possessing 

 considerable strength, is much weaker than the original rock. They also tend to 

 show that when the deformation is carried on slowly the resulting rock is stronger 

 than when the deformation is rapid. 



Thin-sections of the deformed marble, 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 wliich had taken 

 place. The deformed })ortion of the rock can be at once distinguished by its turbid 

 appearance, differing in a marked manner from the clear transparent mosaic of 

 the unaltered cone. This turbid appearance is most marked along a series of reticu- 

 lating lines running through the sections, which when highly magnified are seen 

 to consist of lines or bands of minute calcite granules. They are 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 

 remain as a compact mass after the movement ceased. In this granulated material 

 are inclosed great numbers of irregular fragments and shreds of calcite crystals, 

 bent and twisted, which have been carried along in the moving mass of granulated 

 calcite as the shearing progressed. This structure is therefore cataclastic, and is 

 identical with that seen in the feldspars of many gneisses. 



Between these lines of granulated material the marble shows movements of 

 another sort. Most of the calcite individuals in tliese positions canbe 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 poly- 



