THE STRUCTURAL CLASSIFICATION 583 



4. Several so-called oil pools or scums of oil found on the surface of the 

 Gulf of Mexico and plotted on the maps of the Hydrographic Bureau agree 

 most remarkably in parallelism with the Five Islands. 



5. Harris gives I. N. Knapp credit for the theory that the line formed by 

 the Five Islands marks the location of a slight anticline, and Harris also states 

 that the lower course of the Mississippi River from some distance above Baton 

 Rouge to its mouth is determined by a syncline. 



6. The strata of the Vicksburg formation seem to have been deposited in a 

 V-shaped area whose limbs correspond with the two general systems. 



7. The isogonic lines, or lines of terrestrial magnetism, are somewhat drawn 

 together along the Sabine uplift, and this is believed by Harris to account for 

 structural complications in that vicinity. 



Harris grouped the supposed faults into two systems, one of them being 

 roughly parallel to the Red Eiver fault and the Alabama Landing fault, 

 and the second roughly parallel with the Balcones fault in Texas. Since 

 the evidence for the existence of these two series is far from conclusive, 

 other possible groupings are suggested here which may or may not be 

 true. A most interesting coincidence seems to be that the Anse la Butte, 

 Jennings, Welsh, Sulphur, and Sour Lake domes are all situated on an 

 east-west line, which appears perfectly straight and is more conspicuous 

 than some of Harris's lines. It would be equally possible to plot a line 

 from the Vinton, Spindletop, Barbers, Blue liidge, and Welsh domes. 



Whatever may be thought of the possibility of geological predictions 

 in a flat country like southern Louisiana, it must be acknowledged that 

 all the Gulf Coast pools arc situated on the saline dome type of structure, 

 and that many of these wliich contain oil lie on absolutely straight lines. 

 In the entire Gulf Coast region not a single instance of success is re- 

 corded outside of a dome. 



Origin of saline domes. — At least five different theories have been pro- 

 posed at various times to account for the origin of the Texas-Louisiana 

 domes. These are as follows : 



1. That the domes are old Cretaceous peaks left as monadnocks by 

 denudation which cut down the surrounding country. The limited hori- 

 zontal extent of the salt masses is good evidence against this theory, as 

 the domes are so isolated and local that they can hardly be parts of dis- 

 sected ridges. 



2. That they originated by gas pressure. 



3. That they originated by water pressure. 



4. That the strata were bent upward by laccoliths. This theory was 

 first proposed by Hager,''- and would appear to find support in the exist- 

 ence of volcanic plugs of Subclass IV(e) in the Coastal Plain of Mexico, 



Lee Ilager : Eng. and Min. Jour., vol. 78, 1904, pp. 137-139 and 180-183. 



