Data obtained from recent intensive and deep drilling on piercement salt domes of southern Louisiana demonstrate that many salt domes of that area exhibit structural configurations which differ considerably from those conforming with generally accepted concepts of salt-dome growth and from results of scale-model studies. The domal cores of many of the salt-dome structures of the lower Gulf Coast are composed of intrusive salt and contorted, brecciated, intrusive shale, of deep-water marine facies of diverse age, which is encountered stratigraphically and structurally far above its normal position. Where present, this intrusive deep-water marine shale, termed "diapiric shale" in a system of terminology proposed herein, performs the same function as does the salt core itself in providing the upstructure seal against which the less disturbed bedded sands and shales pinch out and terminate. The diapiric shale is interpreted as having breached, just as has the salt, the overlying sediments as a result of the impetus imparted to it by the buoyant energy of the associated diapiric salt. A study of the Valentine dome of southeastern Louisiana presents a good example of the nature of the domal core of many of the salt domes of this region; the diapiric shale component of this domal core has actually flowed higher than has the diapiric salt, showing its intrusive nature and demonstrating that it has not merely been dragged upward by the intrusive salt core. Evidence is presented which suggests that some salt-dome structures have been developed by differential vertical movement, at various times, of localized parts of the domal core, as well as by a shift in locus of the center of uplift.