44 GEOLOGY AND MINERAL RESOURCES OF MISSISSIPPI. 
position of the Grand Gulf strata can rarely be shown to be otherwise than nearly or quite 
horizontal on the average, although in many cases faults or subsidences have caused them 
to dip, sometimes quite steeply, in almost any direction." 
After a study of the Grand Gulf strata along Chickasawhay River north of its confluence 
with Leaf River Doctor Smith, in an unpublished essay on the later Tertiary strata, reaches 
the conclusion that there is but little, if any, dip to the Grand Gulf. He further says, how- 
ever, that the calcareous strata outcropping on the Chickasawhay a few miles above the 
mouth of Leaf River and bearing Miocene fossils at the base of the lignitic clays which Ilil- 
gard called Grand Gulf, are found in a well at Mobile at a depth of 700 feet. The conflu- 
ence of these two rivers is but about 25 miles north of the latitude of Mobile. On this evi- 
dence, therefore, and apparently somewhat at variance with the statement made by Smith 
that the strata along the Chickasawhay "are nearly or quite horizontal," there is a south- 
ward dip of at least 20 feet to the mile, ample allowance being made for difference in eleva- 
tion of the two places. A much greater southward dip is obtained from beds containing 
Miocene fossils on Chattahoochee River, extending from Chattahoochee Landing down to 
Alum Bluff. "The Chattahoochee Miocene [Oligocene of this paper] beds," says Smith, 
"outcrop at least in one place in Alabama, viz, on Conecuh River, in Escambia County, 
above Roberts, and about Roberts post-office. But deep borings in Mobile (30 miles south 
of Roberts) have shown that the very same beds that occur along Chattahoochee River lie 
at a depth of 1 ,5.50 feet, more or less, below the surface. Many well-preserved shells brought 
up from this depth afford ample proof of this." If the Miocene beds continue westward 
across Alabama from Chattahoochee River, which is very probable, the southward dip is 
thus something like 50 feet to the mile. 
It seems probable, then, that there is a very steep southerly dip to the older Tertiary, 
including the Chattahoochee Oligocene and overlying Miocene beds, but that on coming 
upward to the Grand Gulf strata the southerly dip has almost and in some places entirely 
disappeared. The deposition of the Grand Gulf strata did not immediately follow that of 
the Miocene beds, but there is a marked unconformity and a long time interval between the 
two. There was a marked subsidence of the land during the early part of the Grand Gulf 
period, so that Grand Gulf strata overlapped not only the Miocene beds, but likewise the 
Vieksburg, Jackson, and Claiborne, and extended the blanket far to the north, in places 
overlapping the Cretaceous. 
Smith, in the above-mentioned essay, says that — 
Hflgard saw no contact of the Grand Gulf along its northern border with anything below it other than 
the Vieksburg; but in Alabama, to the east of the Louisville and Nashville Railroad, the northern 
border of this formation takes a turn toward the northeast, and I have seen it resting on not only Vieks- 
burg, but in turn on the Claiborne, on the Buhrstonc, and on the Lignitic formations, even the lowest of 
them at Clayton, in Barbour County; and farther east in BarbourCounty and still more in Georgia 
the Grand Gulf beds lap over well upon the Cretaceous beds. Certainly, therefore, the order of succes- 
sion going southward can not be taken as determining the geologic succession. 
In Alalia ma the blanketing character of the formation is very clearly seen, for in the different parts of 
the northern border of its occurrence erosion has exposed the underlying Tertiary beds, which are 
Vieksburg, Claiborne, Buhrstone, Lignitic Clayton, and even Cretaceous, according to the locality. 
Farther south erosion in similar manner has exposed the underlying Miocene [OligoceneJ in the vicinity 
of Roberts, Ala., and along Chattahoochee River. We may state further that at Mobile, where 
the (hand Gulf beds occupy the surface, capped, it is true, with the Lafayette, the deep wells have dem- 
onstrated the existence at 700 feet below the surface of the Pascagoula bed and at 1,550 feet the Chatta- 
hoochee Miocene [Oligocene], fully determined by the well-preserved shells. At present, then, the 
map of Mississippi must remain, as regards the Grand Gulf, practically as Ililgard has given it, with the 
understanding that the other marine Miocene deposits in all probability underlie and are hidden by it 
as by a blanket. 
QUATERNARY. 
LAFAYETTE FORMATION. 
The Lafayette formation was first described by Ililgard in his Geology and Agriculture of 
Mississippi, in 1860, under the name of Orange sand. The name had previously been used 
by SafTord" of Tennessee, for the present Lafayette, but he included in it the present Wilcox 
Geologic Reconnaissance of Tennessee, 1856, pp. 148, 162. 
