STRUCTURAL CONDITIONS 



441 



northern part of the field, and figure 6 shows photomicrograph of a slide 

 taken from this specimen. The schistose character of this marble has 

 been noted by Van Hise 4 and by Leith, 5 although the localities cited by 

 them are incorrectly given as from Talladega Mountain, Alabama, and 

 from Talladega Mountain, Georgia. 



The direction of shearing in the marble, as recorded in the slip grooves, 

 is in most localities nearly parallel to the dip. A study by the microscope 



PHY LUTE 



MARBLE 



- FAULT 



Figdee 4. — Diagrammatic Representation of minor Offsets in the Marble Deposit 



The offsets are caused by diagonal faulting and a repetition of the marble outcrop 

 caused by strike faulting. The locality is near Herd quarry 



of thin sections of the marble cut in different directions in a plane per- 

 pendicular to the bedding also shows that the greatest elongation of the 

 calcite crystals is parallel to the slip direction. In many cases also a 

 microscopic study of thin-sections taken from well within the sound 

 marble block shows the calcite crystals to have a distinct elongation. 



Joints. — Both tension and compression joints are well represented in 

 the marble (see figure 7). The compression joints, which are the ones; 

 oblique to the strike, are usually the more important ones. In some locali- ! 



4 Charles R. Van Hise: U. S. Geological Survey, Monograph 47, pp. 810-811. 

 6 C. K. Leith : Bull. 239, U. S. Geological Survey, p. 41, pi. 16, 



