JOINTAGE AND THE STRAIN ELLIPSOID 



671 



systems in the plane of the section is to divide the granitic rock quite 

 regularly into large and small rhomboidal joint blocks, crossed by 

 the less conspicuous fractures of the steep joint system, as illustrated 

 in Figures i, 2, and 3. 



Fig. I. — Jointage in granodiorite. Looking north. The steep joint system is 

 indicated by aplite dikes. The heavy inclined joints dip east and are intersected by 

 a third system dipping to the left, only faintly seen in this exposure. 



Very frequently the steep joints with their accompanying dikes 

 are slightly offset along the fractures of the east-dipping inclined 

 set, the strongest set of the three, so that this set is really a series 

 of small thrusts with minute throw, as shown in Figures 2 and 3. 



