In a great many models constructed of various materials and analyzed in accordance with the theory of scale models, asphalt was the most nearly satisfactory material found to represent the salt, and weak muds of greater density than the asphalt were found to be best suited to represent the sedimentary overburden above the salt. The motivating force causing the upward growth of the model domes was produced by the contrast in the densities of the materials.

Single domes were initiated in the laboratory by irregularities on the original asphalt surface, variations in overburden thickness, lateral variations in overburden density, deformation which produced normal faulting of the overburden, and by folding resulting from externally applied forces. The flowage of material into a dome produced a peripheral sink in the asphalt, which in turn caused the initiation of a group of secondary domes in a nearly circular arrangement about the margins of the sink. It appears, therefore, that it is not necessary to call upon a separate geologic event to account for the initiation of each known salt dome. Furthermore, no linear arrangement of salt domes should be expected if many domes are of secondary origin.

The diameters of the model domes were approximately equal to the thickness of the source layers from which they developed. Attempts to form domes with large diameters from thin source beds were entirely unsuccessful. If a similar relationship between dome diameter and source-bed thickness exists in sedimentary basins, the source layer of salt in the salt-dome provinces of the Gulf Coastal Plain must be several thousands of feet thick.

When the thickness of overburden above the top of a model dome exceeded a certain value, no further movement of the dome occurred provided that the overburden had a finite shear strength. The actual thickness required to prevent the growth of a dome depended on the height of the dome above its source layer, the density contrast between the overburden and the salt equivalent, and the strength of the overburden. In the models that were considered to be most nearly dimensionally correct, this critical thickness was approximately the same as the height of the dome above its source layer.

Although the model domes displayed a variety of shapes in the early stages of their development, depending on the method of initiation employed, they became circular in horizontal cross section as they grew upward through successive layers of overburden. When the top of an asphalt dome entered overburden layers of low strength and low density near the surface of a model, the upper part of the dome commonly increased in diameter.

The overburden was arched and fractured by the growth of the model domes. Beds penetrated by the asphalt core were broken by radial fractures, and the nearly triangular segments between these fractures were upturned by the rising asphalt. Layers above the core were arched and broken by normal faults. Grabens over the centers of many of the domes occurred as a result of the greater uplift of marginal fault segments; radial faults were numerous. The fault patterns in the models were controlled by the size and shape of the core, the depth of the core beneath the faulted layer, the amount of uplift of that layer, the configuration of the peripheral sink, and the physical properties of the overburden.