LAFAYETTE FORMATION. 45 
and the whole was referred to the Cretaceous. In 1891 W J McGee a published a paper on 
the Lafayette formation. He likewise included in the term Lafayette 200 feet or more of the 
Wilcox which belongs to the Eocene. The vast deposits of pottery clays in the vicinity of 
Holly Springs, Miss., which contain numerous impressions of leaves of Tertiary plants, were 
improperly placed in the Lafayette by McGee. The term as used in this report is restricted 
to the thin veneering of iron-stained pebbles and sand which overlaps unconformably all the 
other formations of the State, from the older Paleozoic rocks along Tennessee River to and 
including the Grand Gulf group of the late Miocene, and underlies the Port Hudson in 
southern Mississippi. In age it is, therefore, between the Grand Gulf and the Port Hudson 
and loess. In the south the Lafayette is overlain by the Port Hudson clays, while in north- 
ern Mississippi the loess, when present, rests directly on the Lafayette, and the Port Hudson 
is absent. East of the typical calcareous loess in western Mississippi the yellow loam or 
upper member of the loess immediately overlies the Lafayette. In the central and eastern 
parts of the State, where not carried away by erosion, the Lafayette occupies the surface, as 
the loess does not extend more than 100 miles from Mississippi River. 
The Lafayette is a fresh-water deposit, which is composed principally of dark-red to faint- 
orange, coarse, round-grained sand, and in places contains more or less clay and waterworn 
pebbles. The pebbles arc of two kinds (a) chert and limestone containing numerous 
Paleozoic fossils, such as fenestellids, favosites, pentremites, and other forms; (b) less numer- 
ous but more resistant quartz pebbles. The former class is much more abundant. They 
were washed into the Lafayette waters from the adjacent Paleozoic hills, as their fossils 
clearly indicate. The nearness of their origin is further indicated by the angular character 
of the pebbles, some of them barely having their sharp corners worn off. The quartz peb- 
bles are all round or egg-shaped and are much smaller than those of Paleozoic ongin. They 
have been transported over a greater distance and are consequently more worn. They are 
doubtless the fragments of the great northern drift carried southward by great volumes of 
cold, fresh water at the close of the Glacial epoch. 
The thickness of the formation varies from a knife-edge to 50 feet. The latter, however, is 
very rare. It is more often found to be less than 10 feet thick. 
In Tishomingo and Itawamba counties the Lafayette contains large deposits of water- 
worn pebbles of flint, chert, and quartz. Another belt of similar material, but somewhat 
different in the shape of the pebbles, occurs along the eastern edge of the loess formation, 
comprising the counties of De Soto, Tate, and Yalobusha. The pebbles of the northeastern 
area are oblong or egg shaped and contain more quartz, while those of the western area are 
worn into a more rounded form. Still another belt, which is practically a prolongation of 
the western belt, is found in the southern part of the State, the main line of the Illinois Cen- 
tral Railroad following along the outcrop of the gravel beds from Jackson to the Louisiana 
border. 
The Lafayette was deposited upon a deeply eroded surface of the older formations, which 
accounts in part for the irregularity of its thickness. In some places gullies and ravines, cut 
in the old formations and filled with Lafayette, have been exposed. Since the deposition of 
the Lafayette there has been a large amount of erosion and in many areas the whole forma- 
tion has been removed. In the Selma chalk and Porters Creek areas the Lafayette is gener- 
ally absent, when present it occurs in small isolated patches. East of the Selma chalk area 
there is more or less Lafayette covering the Eutaw and Tuscaloosa and overlapping onto the 
Carboniferous. In northern Mississippi, particularly in Marshall and Lafayette counties, 
where the formation was first described and named, the Lafayette, when present, is but a 
few feet thick, but in most places it is wanting. It thickens to the south, reaching its maxi- 
mum thickness, said to be 200 feet, in southern Mississippi. No such thickness, however, 
was observed in the course of the present work. 
In various localities over the State the iron in the Lafayette has cemented the yellow or 
red sands into a ferruginous sandstone, which contains more or less iron and is often mis- 
taken for pure limonite or brown hematite. These deposits are in every case of very shal- 
a Twelfth Ann. Rept. U. S. Geol. Survey, pt. 1, 1891, pp. 353-521. 
