A NOTE ON JOINTAGE AND THE APPLICATION 

 OF THE STRAIN ELLIPSOID 



ROY R. MORSE 

 University of California 



INTRODUCTION 



In conducting a class in field geology across a portion of the 

 superb section exposed in the walls of Merced Canyon, just below 

 the Yosemite Valley, the writer recently observed an interesting 

 case of jointage which appears to deserve note. 



The section at its upper end includes the massive exposures of 

 the granitic rock of the Sierra batholith, such as in the sheer wall of 

 El Capitan and adjacent exposures, and it extends down the canyon 

 of the Merced across the western margin of the batholith and into 

 the adjoining belt of metamorphic rocks. 



DISTRIBUTION OF THE JOINTS 



The jointage here considered is best developed and most con- 

 spicuous on the immediate margin of the plutonic mass, though 

 jointing is by no means restricted to this portion of the section. 



In the massive walls of the Yosemite Valley strong and persistent 

 joints are to be seen. Some are very steep, some inclined at moder- 

 ate angles, still others are at low angles. No attempt was made to 

 study these in detail, but one gets the impression from the floor of 

 the valley that the moderately inclined joints, dipping both easterly 

 and westerly, are somewhat more conspicuous than the others. 

 In this upper portion of the section, some lo miles from the western 

 margin of the batholith, the joints are as a rule widely spaced and 

 the . rock loses none of its massive character as a result of the 

 fracturing. 



Here the average rock type is a medium-grained light-colored 

 granodiorite. As one proceeds down the canyon, toward the outer 

 portion of the granitic mass, changes in both composition and 



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