32 C. R. VAN HISE 



these ruptures occur close together, and there is slight differen- 

 tial movement, a distributive displacement may be produced, 

 which is equivalent to a reverse fault, and which therefore results 

 in crustal shortening, or the distributive displacements may be 

 similar to those of the shearing joints of figure 10 and therefore 

 result in crustal elongation. However, as in the case of cleavage 

 just described, a region which is under compressive tangential 

 stresses, and therefore is deformed by distributive faulting paral- 

 lel to fissility, may later be under conditions of tensile tangen- 

 tial stresses. In this case partings will occur between the fissile 

 laminae, and elongation result. These elongations are strictly 

 analogous to the elongation of normal faulting. The openings 

 may be closed, as in the case of normal faulting, by a dropping 

 down of the overhanging strata, or by methods of injection or 

 cementation, as explained below. 



Minute normal fault slips, secondary to cleavage or fissility, 

 have been observed in the crystalline rocks near Blowing 

 Rock, N. C. While during the formation of cleavage or fissil- 

 ity it is probable that shortening took place, it cannot be 

 asserted that the subsequent elongation did not compensate for 

 this, and it cannot be ascertained whether the total effect of the 

 various deformations in this district resulted in elongation or 

 shortening. 



Vtdcanism and cementation. — After a secondary structure has 

 been produced, whether it be cleavage, fissility, joint, fault, or 

 irregular structure, it may be taken advantage of by igneous 

 intrusions in connection with deformation. These injections 

 with the assistance of orogenic movements may greatly widen the 

 openings so as to make places for great dikes. Such injections 

 result in the local elongation of the crust of the earth. The 

 injections may be divided into two classes, regular, approxi- 

 mately parallel injections, which take advantage of the above 

 regular structures, and irregular injections. 



Throughout considerable districts the amount of parallel 

 injected materials is equal to, or surpasses the amount of orig- 

 inal materials in which the regular secondary structures were 





