580 F. G. CLAPP CLASSIFICATION OF PETROLEUM AND GAS FIELDS 



may stand practically vertical on its circumference. An uplift of several 

 thousand feet in an area a mile across is not uncommon. While no Cre- 

 taceous beds of normal structure reach the surface in Louisiana, there 

 are several saline domes in which these formations have been uplifted to 

 the surface in limited areas. Beneath the Cretaceous beds and inter- 

 laminated with them in the center of the domes are found extensive de- 

 posits of rock-salt, sulphur, g3^psum, and sometimes other minerals. 



The term "dome," therefore, refers to the geological structure, as illus- 

 trated in figure 11, and in the Gulf Coast oil fields the underlying forma- 

 tions are domed, whether the surface is so or not. At Spindletop the 

 rock structure has been carefully determined on the basis of well records 

 and found to have a form similar to that illustrated. The cross-sections 

 of all saline domes, so far as determined, show a similar, more or less 

 dome-like form, although great differences exist in local conditions. As a 

 rule, sands and gravels are penetrated for several hundred feet in depth, 

 then limestone or dolomite is encountered, below which sulphur, gypsum, 

 and rock-salt are found. The character of these minerals is not supposed 

 to have any effect on the existence of oil at the particular point; but the 

 oil has been accumulated from the surrounding strata either because of a 

 point of interruption formed by the upward doming of the sediments or 

 because the breaking of the strata have allowed it to rise from below. 



List of known saline domes. — Practically all the known saline domes 

 except those discovered within the past eight years have been described 

 and mapped by Yeatch^* and Harris.^-^ The following list comprises 

 some of the salines in Louisiana: Grand Cote (Weeks Islatid), Petite 

 Anse (Averys Island), Belle Isle, Cote Blanche, Cote Carline (Jeffersons 

 Island), Anse la Butte, Prairie Mamou (Jennings oil field), Welsh, 

 Chicot (Pine Prairie), Sulphur, Vinton, Hacksberry, Negreet saline, 

 Coal Bluff saline. Many, Bayou Castor saline. Browns saline, Cedar Bayou 

 saline, Winnfield dome, Coochie dome. Drakes saline, Prices saline, Rey- 

 burns saline, and Bistineau saline. 



Some of the saline domes in Texas are as follows : Davis Hill, Saratoga, 

 Batson, Big Hill, in Jefferson County ; Sour Lake, Spindletop, Big Hill, 

 in Matagorda County ; Dayton, Humble, Barbers Hill, High Island, Blue 

 Eidge, Hoskins Mound, Damons Mound, Kaisers Hill, Bryan Heights, 

 Grand saline, Palestine, Steens saline. Brooks saline, Grahams saline, 

 Markham, and Stivers saline. 



Association of rock-salt and other minerals. — Salt is believed to exist 

 in all domes of this subclass. The salt consists of 98 to 99 per cent 



5* A. C. Veatch : La. Geol. Survey, Rept. 1902, pp. 41-100. 

 55 Bull. 429, U. S. Geol. Survey, 1910. 



