ROCK FLO WAGE AND MASHING. 763 



better than any other the macroscopical point of view of the zone of flow. 

 Without further exposition, which would involve repetition, I propose the 

 term "mashing" to cover mass deformations of all kinds in the zone of rock 

 flow. 



The term "mashing-," thus used, includes much of the process which 

 has usually been described under the terms "dynamic metamorphism" and 

 "shearing*." The term "dynamic metamorphism" is objectionable for 

 many reasons; it will here simply be said that fracturing in the belt of 

 cementation is equally dynamic metamorphism ; but the effects in the two 

 zones of flowage and fracture contrast so sharply that they should not be 

 confused. The term "shearing" has been used in a very loose and most 

 objectionable manner. Most authors who have used it mean differential 

 movement along a certain set of parallel planes, but apparently most 

 geologists who have thus used the term do not recognize that shearing 

 parallel to one plane is invariably accompanied by shearing in other planes. 

 Nor is it generally understood that when rocks are compressed by short- 

 ening without rotation this is possible only by shearing along all sets of 

 diagonal intersecting planes. In short, in all cases which have been 

 described as shearing and as shortening there is maximum shearing along 

 two sets of intersecting planes and maximum shortening and elongation in 

 the two directions half way between the two sets of shearing planes. 

 Further, as the term "shearing" is ordinarily used, it seems to be assumed 

 that there results a structure parallel to the one set of shearing planes, 

 whereas this may or may not be true." Therefore, to avoid errors implied 

 by the terms "dynamic metamorphism" and "shearing,"' the term "mash- 

 ing " is introduced, and from this term the implications which attach to the 

 others have been excluded. 



In this connection it should be noted that mashed rocks and their 

 constituent portions, such as pebbles and minerals, are frequently spoken 

 of as stretched. For the most part, this term can not be applied to rocks 

 in the same manner that it is applied to india rubber or steel. In general, 

 the facts upon which the statements as to stretching are made are simply 

 that the rocks show evidence of being longer in a certain direction than 

 they were originally. However, it does not follow from this that the rocks 



"Hoskins, L. M., Flow and fracture of rocks as related to structure; appendix to Van Hise, C. R., 

 Principles of North American pre-Cambrian geology: Sixteenth Ann. Rept. U. S. Geol. Survey, pt. 1, 

 1896, pp. 860-866. 



