proceedings: geoIvOGical societv 289 



informal communications 



T. W. Vaughn: Correlation of Tertiary formations on the perimeter 

 of the Carrihean Sea. 



R. S. BassIvEr: Quartz from Waynesboro formation crystallizing 

 with three-faced terminal pyramid and used for correlation. 



REGULAR PROGR.\M 



Ralph Arnold : The economic value of paleontology. 

 E. W. Shaw: Stratigraphy of the Gulf Coastal Plain as related to 

 salt domes. 



This paper being in a way introductory to the following paper on 

 the program has to do primarily with those features of the stratigraphy 

 that are of principal interest in the study of salt domes. The more sig- 

 nificant of these features relate to the age and thickness of the forma- 

 tions, and to the rigidity, chemical nature, and specific gravity of the 

 materials composing them. 



As is well known the formations are of Mesozoic and Cenozoic age 

 and with the exception of the Jurassic most of the main divisions of 

 these eras are known to be represented by deposits. Perhaps the 

 divisions of the Cenozoic are more fully represented than those of the 

 Mesozoic. 



The aggregate thickness of the Cenozoic is commonly between 5000 

 and 7000 feet, the Eocene being 2500 to 3000, Oligocene and Miocene 

 2000 to 2500, and the Pliocene and Quaternary from 1000 to 3000. The 

 upper Cretaceous seems to have the thickness ranging from 1500 to 

 2500 and the lower Cretaceous, where present, from a feather edge to 

 about a thousand feet. Over a large area in coastal Louisiana and 

 Texas the aggregate thickness of the various Cretaceous, Tertiary, and 

 Quaternary formations probably ranges between 8000 and 12,000 feet 

 and may average about 10,000 feet. 



Apparently most of formations thicken somewhat toward the coast 

 but the average or aggregate amount of thickening is unknown. To 

 the east there is a notable thinning and rise of certain formations at 

 least; beds lying at a depth of 2000 feet near Mobile lie at far greater 

 depths two hundred miles to the west and a similar distance from the 

 coast. 



The age and nature of the materials underlying the Cretaceous along 

 the Gulf Coast can only be conjectured. Knowledge concerning these 

 materials and in particular as to whether or not they include beds or 

 masses of salt and intrusions of igneous rock might be of considerable 

 assistance in solving the salt dome problem. In central and western 

 Texas the Triassic and Permian beds are many hundred feet thick and 

 are salt bearing but they dip to the west and without reversal can not 

 be present in Louisiana. Neither this nor any other known fact proves 

 that there are no Permian or Triassic salt beds under Louisiana, but on 

 the other hand the only reason for suspecting that they are present is 

 the conclusion that the salt, gypsum, dolomite, sulphur, and other 

 mineral matter in the salt dome came from below and the fact that 

 such mineral matter is perhaps more common in the Permian and Tri- 



