26 RESOURCES OF TENNESSEE. 



After another considerable lapse of time, the sea again en- 

 croached upon the Embayment area. On the Arkansas side, 

 it seems to have extended further west than it did during the 

 Upper Cretaceous advance, and it reached equally as far north ; 

 but in Tennessee it perhaps did not reach so far east as did the 

 Cretaceous sea. This was during Tertiary times. The inva- 

 sion was much interrupted, the shore line having shifted back 

 and forth over the area many times.* The deposits then put 

 down are of Tertiary age. As a result of this shifting, the 

 deposits are much complicated, and the several divisions are 

 now known under as many different names, but for the sake 

 of simplicity they will here be described under their old names, 

 the Porters Creek and Lagrange formations. After the depo- 

 sition of the younger of these formations, the sea again re- 

 treated, again leaving the area as dry land. 



There are gravels and sands, generally known as the Lafay- 

 ette formation, over more or less of the area, but the origin of 

 these is in doubt. For this reason, and because this and a yet 

 younger formation that occurs along the Mississippi River, 

 known as loess, do not enter into the problem of oil and gas, 

 they will not be considered further. 



Cretaceous formations of Tennessee. The Cretaceous de- 

 posits of the Embayment area are mainly of Upper Cretaceous 

 age. They have been described by the late Dr. James M. Saf- 

 ford in the Geology of Tennessee, by Dr. L. C. Glenn**, by Dr. 

 L. W. Stephenson,f and others. $ 



For the purpose of description, the lowest part of the Creta- 

 ceous deposits in Tennessee may be called the Eutaw sand, that 

 being the name by which it has been known in recent years. 



*Berry, E. W., U. S. Geol. Surv., Prof. Paper, 95-F. 

 **U. S. Geol. Surv. Water Supply and Irrigation Paper, No. 164. 



tU. S. Geol. Surv., Prof. Paper, No. 81. 



JMr. Bruce Wade is making a careful study of these deposits for this Sur- 

 vey, but his work is not yet finished, and no part of his results have been 

 published. 



The work lately done by Messrs. H. D. Miser and L. W. Stephenson of 

 the U. S. Geological Survey and Mr. Bruce Wade of this Survey, indicates 

 that the lower part of what is here called Eutaw sand, is Tuscaloosa, a 

 formation well developed in Alabama, but less so in Tennessee. Its most 

 conspicuous development in Tennessee is on the hills east of Tennessee River. 

 It is considered of Lower Cretaceous age. 



