DEVELOPMErX OF THE DISCOIDAL HYPOTHESIS 291 



foliation, the rotation finds a ready explanation. The mechanics of move- 

 ment, uplift, and vulcanism constitute an accordant group of phenomena 

 under this hA-pothesis.*^ 



SUBOCEANIC CONDITIONS OF FOLIATION 



In the preceding section the stress which is regarded as competent to 

 orient foliation is due to the unloading and loading effects of erosion. 

 The area beneath which the stress develops is evidenth' the elevated land 

 which is eroded and any hollow in which the sediments are deposited. 

 The latter may be continental or suboceanic. If the loaded belt be sub- 

 marine, it is commonly narrow as compared with the extent of the basin. 

 Beyond it lie great expanses of the ocean floor, where the loading is 

 insignificant. Within these areas lie the greater deeps, and therefore, by 

 postulate of isostasy, the greater densities. What of the orientation of 

 foliation in these extensive regions where erosion and sedimentation are 

 absent or negligible ? 



Any answer to this question, in order to be consistent with the basal 

 hypothesis of the discussion, must be framed on the assumption that the 

 underbodies of the deeps have reached their present position in the effort 

 to attain isostatic equilibrium. If, at any stage of development of the 

 ocean basins, the underbodies stood too high w4th reference to the sur- 

 rounding masses, they must have sunk to their present depressed posi- 

 tions. The stresses developed before and during subsidence must have 

 been directed horizontally outward, and in the adjacent masses upward. 

 Any adjustment by recrystallization of the solid substance would, there- 

 fore, result in an accordant foliation. 



It would appear that this reasoning is conclusiA^e, provided the under- 

 bodies of the deeps have assumed their low positions by sinking from 

 higher ones. If, however, they have risen from lower ones or tend to 

 do so, the resultant stresses and foliation would be directed upward within 

 them and would be directed outward toward them in the neighboring 

 masses, since the latter would have sunk as the deeps rose till equilibrium 

 w^s reached. 



The latter postulate does not accord readily with any process of gravi- 

 tative accumulation of the denser and lighter masses. It, the postulate 

 of an original overdeepened basin, seems in general less probable than 

 that of original overburdened areas; and this inference is confirmed if 

 we consider the distribution of igneous outcrops, which are grouped 

 around rather than conspicuously in ocean basins. The latter would be 



" To be discussed in an article on the mechanics of the Pacific ranges, to appear in 

 the Chicago .Tournal of Geology. 



