486 



SCIENCE. 



[N. S. Vol. XXIII. No. 587. 



a small percentage (not more than one 

 one hundredth of one per cent, according 

 to Dr. Harper) of the rocks of the series, 

 eastward of Flint River. 



From this northern border it may be 

 traced southward to the southern limit of 

 the state, and beyond, at least to Chatta- 

 hoochee in Florida, where it occupies as 

 usual, the summit of the plateau with only 

 the red loam and pebbles of the Lafayette 

 over it; and along the road leading do'WTi 

 from this plateau to the Old Chattahoochee 

 Landing, it may be seen resting directly 

 upon the Miocene limestone first identified 

 as such by Langdon as above mentioned. 



While our recent observations have not 

 extended any further south along the 

 Chattahoochee than this point, we have 

 good reason for the belief that the same 

 Grand Gulf and Lafayette mantle occupies 

 the summit of Alum Bluff itself. 



Keeping in mind the fact that the Grand 

 Gulf mottled clays overlie directly the 

 Miocene limestone at Chattahoochee Land- 

 ing, let us consider what the deep borings at 

 Mobile, at Alabama Port, Mobile Coiinty, 

 and at Bon Secours Bay in Baldwin 

 County, reveal. In all these wells, with 

 the Grand Gulf capped with the Lafayette 

 forming the surface, the Gnathodon bed 

 of the Pascagoula Pliocene is penetrated 

 at the depth of 700 to 800 feet; and be- 

 low that, to the depth of 1,600 feet, follows 

 a succession of beds with well preserved 

 and easily identifiable shells, characteristic 

 of the several horizons of the Chattahoochee 

 (Miocene) River section. The borings end 

 in these beds before reaching the top of 

 the Vieksburg. 



The most remarkable thing in connection 

 with these later Tertiary strata and that 

 which has cai;sed so much perplexity among 

 the geologists is the rarity of their out- 

 crops at the surface west of the Chatta- 

 hoochee River. There are several known 

 exposures in west Florida already noticed, 



i. e., on Chipola River, Shoal River and at 

 Oak Grove; only one locality has as yet 

 been noticed in Alabama, i. e., on Conecuh 

 River near Roberts in Escambia County; 

 only one in Mississippi, viz., that of the 

 gnathodon bed near Merrill on Chicka- 

 sawhay River. We hear of none in Louis- 

 iana, and none in Texas; yet in the latter 

 state the deep borings at Galveston and 

 Beaumont, after passing through 458 feet 

 of recent and Pleistocene strata, and 1,035 

 feet of beds of doubtful age, penetrate at 

 least 650 feet of beds referred to the Upper 

 Tertiary, and 917 feet of beds containing 

 characteristic shells of Miocene age.^ We 

 know the reason of this in Alabama, for 

 the surface of the country here in which 

 they should outcrop is covered by an un- 

 determined thickness of the beds of the 

 Grand Gulf and Lafayette. Probably the 

 same explanation would apply to the other 

 states. 



From the facts detailed above, the con- 

 clusion seems unavoidable that the Grand 

 Gulf, lies ahove any Tertiary formation 

 as yet described in the Gulf states; it be- 

 ing, on the testimony of the Mobile wells, 

 at least 700 feet above the Pascagoula beds 

 which from the 0. Virginica which they 

 contain, must be assigned to the Pliocene. 

 The additional fact that no formation 

 older than the Lafayette has yet been ob- 

 served overlying it, betokens its compara- 

 .tively recent age. 



The only escape from the conclusion thus 

 forced upon us seems to be the assumption 

 that Wailes, Hilgard, Hopkins, Lough- 

 ridge, Hill, Kennedy, Dumble and the other 

 geologists who have made this region a 

 study, have been mistaken in their identifi- 

 cations of the Grand Gulf, and have con- 

 founded it with something else. 



Let us, therefore, look at it from an- 

 other point of view. The usual place as- 



° Gilbert D. Harris, Fourth Annual Report, Geo- 

 logical Survey of Texas, 1892, pp. 91-95. 



