STKCCTUKAL CONDITIONS 



443 



ties these diagonal joints have a distinctly radiating character, such as 

 would result from torsional stresses. Such torsional stresses would occur 

 in case of unequal support of the strata or uneven distribution of resist- 

 ance to the compressive forces. Figure 7 shows the nature of the jointing 

 in one of the quarries of the marble area. The lines represented in the 

 figure are the intersection of the jointing planes with the plane of the 

 bed prospected. 



■■■■.'■ ■ 



j i .. 



■ ■ ... ■' ■ • . ,'.... 

 I 



Figure 6. — Photomicrograph of schistose Marble from near Taylors Mill 



The crystals are distinctly elongated. The average maximum grain is about .16 mm., 

 which shows the marble here to be much less metamorphosed than at other places in the 

 field. At the time of metamorphism it must have been less deeply buried, and therefore 

 less easily deformed without shearing than the marbles elsewhere in the field. Magnified 

 50 diameters. Compare with figure 8, which represents marble from Gantts Quarry with 

 same magnification. 



Drag-folding. — Evidence of drag-folding in the marble is frequently 

 seen. In one of the quarries many of the blocks, which are taken out 

 parallel to the general dip direction, show an angle of as much as 15 

 degrees between the minor schist lines in the block and the general bed- 

 ding planes (see figure 9). 



In all exposures the marble is much more unsound at the surface, clue 



