Ever since Balk's studies of the 1940s, the idea has been growing End_Page 2209------------------------------ that the salt of a stock moves vertically upward in several unit cylinders called spines. Observations in the salt mines of the Five Islands trend in south Louisiana confirm this interpretation. In some places the spines are defined by sedimentary gouge (shale, sand, limestone), which becomes included in the salt core and clearly marks the spine boundaries. These boundary shear zones can extend from the edge of the salt to the very center of the stock. Shear zones that have a diameter of 1,000 to 4,000 ft have been observed in four of the five mines. Every gradation exists from relatively simple, thin (15 ft), linear shear zones, to wider (400 ft) ones that have been twisted and sheared into the salt in complicated patterns by later salt movements. The shear zones can be traced upward through the salt to surface irregularities in the salt-stock surface, and into topographic irregularities on the ground surface (generally valleys). Disruptions of the overlying domal sedimentary rocks also can be recognized, and Balk and Muehlberger suggested these as the cause of the irregular salt motion. The present analysis suggests, however, that the salt spines cause the overlying strata disruptions. End_of_Article - Last_Page 2210------------