OIL IN THE REELFOOT AREA. 25 



the deposits of the Embayment area differ from those that sur- 

 round it in being much younger and in consisting for the most 

 part of soft, unconsolidated material, such as sand and clay. 

 The youth of these deposits is due to their having been put 

 down during comparatively recent invasions of the sea, at 

 which times the Gulf lapped over upon the continent, each cov- 

 ering more or less of those parts of Tennessee, Arkansas and 

 the other states above named, as lying within the Embayment 

 area. 



There were several of these invasions of the Gulf. The first 

 one covered the eastern part of Texas; reached up into southern 

 Arkansas, and extended eastward well into Alabama, and at 

 least as far as Wayne County in Tennessee. This was during 

 what is commonly called Lower Cretaceous times, and the de- 

 posits put down in the seas of this time are accordingly of 

 Lower Cretaceous age.f The northern extent of these deposits 

 is not known, because in that direction they are covered by 

 younger formations. In Arkansas and Texas they consist of 

 beds of chalk, limestone, sand, clay and gravel. Where exposed 

 in -Hardin and Wayne counties, Tennessee, they consist of sand 

 and gravel. 



After the Lower Cretaceous beds were deposited, the Gulf 

 retreated to the south, leaving the topmost of those beds form- 

 ing a, land area. The extent of the southward retreat of the 

 shore line is not known. After a considerable lapse of time, 

 it again advanced northward, this time reaching past the pres- 

 ent site of Cairo, 111. This was during what is commonly called 

 Upper Cretaceous* time, and the deposits then put down are 

 of Upper Cretaceous age. These deposits are in three forma- 

 tions, known as the Eutaw sand, the Selma clay, and the Ripley 

 formation. They are important in this connection, for if oil 

 or gas or both, occur in the Embayment area, they are more 

 likely to come from some of these formations than from the 

 younger ones above. They will have more attention later in 

 this paper 



After the deposition of these formations, the sea again with- 

 drew to the south, leaving the younger of these rocks and pos- 

 sibly some of the edges of the older ones as a land area. 



fThis is also called the Comanchean period. Geology, by Thomas C. Cham- 

 berlin and Rollin D. Salisbury. Henry Holt and Company. 

 *Chamberlin and Salisbury call this the Cretaceous period. 



