EFFECT OF ROCK FLO WAGE ON TEXTUEE AND STRUCTURE. 761 



textures of some rocks may be wholly destroyed. For instance, such 

 rocks as quartzose sandstones, composed dominantly of a single mineral, 

 which retain their structures for indefinite periods if there be no marked 

 deformation even when buried under a thousand or more meters of other 

 rocks, when deformed in the zone of anamorphism, rapidly lose all clastic 

 textures. In place of the original textures, whether those of sedimentary or 

 those of igneous rocks, in consequence of flowage there appear the peculiar 

 textures of the slaty, schistose, gneissose, and cataclastic rocks. 



But while there is a marked tendency to obscure and finally to oblit- 

 erate textures and structures by flowage, the extent to which this goes is 

 very variable. The larger the texture or structure the less likely it is to be 

 destroyed. Since structures involve larger masses than textures, the 

 former may not be much obscured at a stage when the textures are 

 wholly gone. 



During rock flowage, even if there be perfect granulation or recrys- 

 tallization, or some combination of the two, the resultant rock may preserve 

 the larger textural and structural units of the original rock. This is more 

 likely to be true of granulation than of recrystallization. In rocks com- 

 posed of a number of minerals, even where granulation is complete, the 

 aggregate of mineral particles resulting from each original mineral particle 

 is commonly preserved as an elongated or flattened disk, the different 

 granules not being mingled to any considerable extent with those of the 

 granules of the associated minerals. For instance, the many granules 

 from a large feldspar grain of anorthosite may constitute an oval area little 

 or not at all mingled with the granules of the adjacent pyroxene. Again, 

 the innumerable granules of a flattened pebble of a conglomerate may be 

 sharply separated from the granules of the adjacent matrix, so that the 

 pebble is easily discriminated. 



In proportion as recrystallization takes place the textures are likely to 

 become more rapidly obscured. The solutions transport material for short 

 distances from one mineral particle to another, and thus the products 

 become intermingled. For instance, adjacent feldspar and pyroxene may 

 produce reaction minerals different from each. But even where recrys- 

 tallization occurs the process must go to an extreme before the flattened 

 pebbles of a coarse conglomerate are wholly lost. Even when the matrix 

 is a coarse schist or gneiss the flattened disks of the pebbles are often 



