Adams db Coker — The Floio of Marble. 485 



defined twinning, giving* rise to the fibrous appearance before 

 described. In some cases a grain showed strain shadows at 

 one end which passed over into a very narrow polysynthetic 

 twinning at the other. The twin lamellae in many cases 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 millimeter ('00001968 inch and 

 •00002361 inch), and some were even narrower. 



While the rock was deformed without loss of strength, the 

 presence of water, so far as could be ascertained, did not influ- 

 ence the character of the deformation. It is just possible, 

 however, that there may have been a deposition of infinitesi- 

 mal amounts of calcium carbonate along very minute cracks or 

 fissures^ thus contributing to maintain the strength of the rock. 

 No signs of such deposition, however, were visible. 



4. Specific gravity of the marble after deformation. 



In order to determine whether as a result of deformation 

 under high differential pressures, the specific gravity of the 

 marble was in any way altered, the specific gravity of two 

 specimens of deformed marble was taken as well as the specific 

 gravity of two specimens of the original rock. 



The first specimen of deformed marble, " A," had been 

 deformed at ordinary temperatures in a tube of nickel steel 

 l cm thick, the experiment being carried out in 100 minutes, 

 the pressure required to effect its deformation being 340,000 

 lbs. to the square inch. The second specimen of deformed 

 marble, " B," had been deformed in a steel tube at a tempera- 

 ture of 400° C. in eight and a half hours at a pressure of 

 63,000 lbs. to the square inch. Both specimens of the 

 deformed marble when placed in water showed at once that 

 they were traversed by minute fissures, as a considerable amount 

 of air was discharged in the form of minute bubbles. Speci- 

 men " A" was allowed to soak in the water until no further 

 bubbles appeared. The rock when so treated was found to 

 have a specific gravity of 2*65. The rock was then placed 

 under water in an air pump. When the pump was worked 

 additional air bubbles appeared, and the rock was allowed to 

 remain under the vacuum until no further air was given off. 

 After this treatment the rock was found to have the specific 

 gravity stated in the accompanying table. In the case of 

 specimen " B," the deformed rock was evidently more solid 

 and compact, as less air was given off. This gives a partial 

 explanation at least for its greater strength, it being evidently 

 freer from minute cracks and fissures. 



The following table shows the specific gravity obtained in 

 the case of the various specimens : 



