658 A TREATISE ON METAMORPHISM. ' 



It lias been said that no lower limit can be given for the zone of anamor- 

 phism. The alterations certainly obey the physical laws of the zone of 

 anamorphism to the depth at which observation is possible as a result of 

 deformation and denudation. How the rocks behave at greater depths is 

 only to be judged by inference. So far as one can foresee the action of 

 the laws of energy, it appears highly probable that the reactions of the 

 zone of anamorphism extend to a very great depth. But in this treatise 

 the zone of anamorphism is restricted to the lower }3art of the lithosphere 

 of which we have observational knowledge, and, following Powell, I apply 

 to the unknown depth below it the term " centrosphere." 



The zone of anamorphism differs in an important respect from that of 

 katamorphism, in that the openings are in general those of subcapillary 

 size. This follows from the fact that the pressure in all directions is 

 greater than the crushing strength of the rocks, and if large openings could 

 be supposed to exist they would be closed by the flowage of the rocks. 

 While the general fact of the subcapillary size of the majority of the open- 

 ings in the zone of anamorphism is beyond doubt, it can not be stated that 

 somewhat larger openings do not exist. So far as there are openings 

 which are filled with liquid that can not escape, the above reasoning does 

 not apply, for the inclosed liquid successfully resists the closing of the 

 cavities. By general reasoning one is not able to determine how large such 

 liquid-filled openings are, but observation indicates that they are small, in 

 general so small that they are observed only by the microscope, and in no 

 cases known to me are they larger. than capillary size. 



One modification of the above statements should be made in reference 

 to openings in the rocks in which the alterations are mainly those of the zone 

 of anamorphism. During- periods of very rapid deformation large fractures 

 may extend much deeper than under ordinary conditions, for whether 

 rupture takes place by major fractures or by flowage is larg-ely dependent 

 upon the speed of the movement. This principle can not be better illus- 

 trated than by the deformation of marble at the surface. Where a marble 

 slab is rapidly deformed at the surface, it is ruptured. Where, however, a 

 similar slab is laid horizontally, being supported only at the ends, so that 

 gravity steadily tends to bend it, the slab bends very slowly with permanent 

 set. This is illustrated in cemeteries by slabs long suspended in the manner 

 described. Julien cites a number of instances of the bending of marble 



