March 30, 1906.] 



SCIENCE. 



485 



the Chattahoochee series, had not been 

 demonstrated as has since been done by 

 many observations, and in reaching the 

 above-mentioned erroneous conclusions re- 

 garding the Miocene age and equivalents 

 of the Grand Gulf, we were dominated by 

 the idea suggested by its relations to the 

 Vieksburg limestone, which it almost every- 

 where immediately overlies, that it must, 

 therefore, be the immediate successor of 

 this limestone in the geological sequence. 



It seems almost impossible to eradicate 

 this belief, not\vithstanding its absolute dis- 

 proof by the records of the Mobile well 

 alone. 



Other equally incontestable, though pei'- 

 haps not quite so obvious, proofs of the 

 true position of the Grand Gulf in the geo- 

 logical column have been obtained by the 

 field investigations in Mississippi, Ala- 

 bama, Florida and Georgia during the 

 years 1900-1904. As long ago as 1860, 

 Dr. Hilgard, that most sagacious of south- 

 ern geologists, described and mapped cor- 

 rectly the Grand Gulf as covering all the 

 lower part of Mississippi from the Vieks- 

 burg outcrop down to within ten miles of 

 the gulf, and with no formation overlying 

 it older than the Stratified Drift or La- 

 fayette. In Alabama, west Florida and 

 Georgia a similar condition of things exists, 

 as will be evident from the following in- 

 stances : 



1. From Healing Springs in Washing- 

 ton County, Ala., down through Mobile 

 County to within a few miles of the gulf, 

 the surface formation is eveiywliere the 

 Grand Gulf with its usual capping of 

 Lafayette. 



2. A little further east in Alabama, begin- 

 ning in Clarke County and coming south- 

 ward through Baldwin to Perdido Baj^, we 

 find again nothing at the surface save 

 Grand Gulf with its Lafayette capping. 

 At Montrose on the eastern shore of Mo- 

 bile Bay and a little below the latitude of 



Mobile, these Grand Gulf clays and sands 

 of the most characteristic type make the 

 Ked Blufif, seventy-five feet in height, with 

 the usual thin capping (fifteen or twenty 

 feet) of Lafayette red loam and pebbles. 

 Continuing on down to the southern end 

 of the county we find the same materials 

 making a bluff, twenty-five or thirty feet 

 in height, washed by the waters of Perdido 

 Bay, i. e., the Gulf of Mexico. So here in 

 Alabama, the Grand Gulf most certainly 

 overlies everything except the Lafayette 

 and more recent strata. 



3. Again along the L. & N. R. R. we 

 have followed the same combination. Grand 

 Gulf with Lafayette capping, from above 

 Evergreen down to Pensacola, where they 

 form a bluff some thirty to forty feet in 

 height overlooking the Bay of Pensacola. 



4. Again in Escambia County, Ala., 

 starting north of the Conecuh River near 

 Roberts, we find -the Grand Gulf overlying 

 and in contact, first with the Vieksburg 

 limestone, then with the Miocene clayey 

 sands which there directly overlie the 

 Vieksburg; then, coming southward into 

 Florida, the same formation with its cap- 

 ping of Lafaj'ette occupies the surface 

 down to the latitude of Oak Grove and be- 

 yond ; the Oak Grove bed with its beautiful 

 Miocene fossils cropping out in the bank 

 of the river, the Grand Gulf on the up- 

 lands one hundred feet above. 



5. Eastward of Escambia County the 

 northern limit of the Grand Gulf laps over 

 formations still older than the Vieksburg, 

 and we see it in Covington County near 

 Andalusia, overlying the Claiborne and the 

 Buhrstone ; and in Barbour County and the 

 adjoining (Quitman) county in Georgia, 

 opposite Eufaula, it overlies the Ripley 

 beds of the Cretaceous. Thence, its land- 

 ward border takes a northeasterly direc- 

 tion, and indurated beds identical with 

 those of the type locality in Mississippi 

 (here called Altamaha Grit) begin to make 



