184 J. BarreU — Relations of Subjacent Igneous 



There is, however, another way in which the crust may 

 be weakened which seems to the writer to be equally im- 

 portant: the weakening from below by the rise along 

 axial zones of orogenic batholiths. Not only is the outer 

 crust dissevered from the inner portion, but the latter 

 may be temporarily destroyed to an unknown degree. 

 The batholithic covers are of irregular form and poorly 

 adapted to resist stresses. It would appear that the ris- 

 ing heated emanations carry high temperatures with them 

 far upward in the crust. The conditions for anamorphic 

 recrystallization may thus be carried to within a mile or 

 two of the surface. The crumpled and foliated struc- 

 tures of the zone of flow and the recrystallization of the 

 rocks may thus not necessarily be restricted to profound 

 depths in the crust. 



Yan Hise located the top of the zone of rock flowage as 

 probably at a depth of five to seven miles, but recognized 

 that it must vary widely with variation in the controlling 

 conditions and would be of least depth for the argillites. 

 F. D. Adams has shown experimentally, however, that 

 cubic compression greatly increased the strength of rocks, 

 and that small cavities could remain open at tempera- 

 tures and pressures such as are found at depths of eleven 

 miles and more in the crust. On the other hand, in east- 

 ern Massachusetts, Carboniferous sediments are trans- 

 formed into schists and sandstone beds are transformed 

 to quartzites; yet these sediments are, so far as 

 known, parts of the last formations deposited before the 

 occurrence of the orogenic revolution which led to their 

 metamorphism. It is not likely that they have ever been 

 profoundly buried, a depth of a mile or at most two miles 

 being the greatest probable depth which can be assumed. 

 In other regions, suggestions of similarly shallow bathol- 

 ithic intrusion are to be f ound,-^ but the generality of this 

 conclusion is founded upon another line of evidence. 



It has been shown by various authors that the soda de- 

 rived from the weathering of plagioclase feldspar is car- 

 ried to the sea, and except for the insignificant amounts 

 precipitated in salt deposits or held in sediments as con- 

 nate waters, it must have accumulated through geological 

 time. But the volume of the sea and its chemical compo- 

 sition are known with fair accuracy. Therefore the vol- 

 ume of the average igneous rock needed to supply the 

 sodium becomes determinable. Allowing one third of the 



-' J. Barren, U. S. Geol. Survey, Prof. Paper 57, p. 166, 1907. 



