362 



University of California. 



[Vol. i. 



in the two portions of the magma which resulted in the two 

 types of structure the crystallization of the orthoclase was simul- 

 taneous, we have an explanation of this curious reversal of sequence 

 of crystallization. If the more basic or nepheline-bearing facies of 

 the laccolite be, as seems very probable, of earlier consolidation 

 than the rest of the magma, the normal sequence of crystallization 

 obtained, and the orthoclase crystallized last, forming a residual 

 mesostasis. But if this portion of the laccolite were in free com- 

 munication with the rest of it, as seems certain, crystallization may 

 have been inaugurated throughout the latter about the time that 

 the orthoclase was forming in the more basic portion. This local 

 crystallization of the orthoclase may be assumed, for lack of a bet- 

 ter hypothesis, to have set up, by a sort of sympathetic action, the 

 general separation of the orthoclase, out of its time, throughout 

 the entire laccolite. 



Geological L aboratoiy, 



University of California, February, i8q6. 



