2G OIL FIELDS OF TEXAS-LOUISIANA COASTAL PLAIN. fBULL.212 
LAFAYETTE SANDS. 
The beds overlying these oil-bearing sands, clays, and limestones 
comprise a series of blue and red thinly laminated and massive red 
and brown clays and cross-bedded sands and gravels having a thick- 
ness of from 30 to 375 feet. They are probably the eastern extension 
of Dumble's Oakville beds of the western division, as they occupy a 
closely analogous position. 
These beds come to the surface and spread over a wide bell to the 
north, overlapping and completely obscuring the petroleum-bearing 
beds. In many places they even overlie and obscure the Frio clays, 
and are found resting direo^ly upon the Fayette sands. These beds 
are widely distributed 1 hroughoul 1 lie Coastal Plain and may probably 
be safely correlated with IMcGee's Lafayette. They have a compara- 
tively gentle dip compared with thai of the underlying Frio clays or 
Fayette sands. 
From the general structure of the country h seems that at the close 
of the Eocene the Frio clays were raised and tilted seaward slightly, 
remaining above water duringthe deposition of the Limestones, sand- 
stones, and clays forming the petroleum-bearing beds. These latter 
were evident Ly Laid down over a sea floor which was being tilted south- 
ward until the last of the petroleum clays, and possibly also some 
of the succeeding red and brown clays of the Lafayette, had been 
deposited. 
This t ill ing movement ceased soon after 1 he beginning of deposit ion 
of the Lafayette, and the land began to sink again. The Lafayette 
sea encroached upon the shores and gradually overran the petroleum- 
bearing beds, deposit Lng sandstones and Limestones, and even covered 
a considerable area occupied by the Frio clays and Fayette sands. 
With another change of movement these red and brown clays and 
gravels were in a Large measure reworked, probably while above sea 
level, and the finer clays and sands were washed into deeper water. 
The coarser material was left by the retiring sea, and now forms the 
extensive deposits of gravel. 
The age of these sands and clays has not yet been satisfactorily 
determined. It is probable that they are in part Miocene and in part 
of later age. They are here assigned to the Miocene, upon the gen- 
eral assumption that they are younger than the Eocene and even the 
oil-bearing beds, but older than any of the Pleistocene deposits. They 
may possibly belong to the Pliocene, although Ave have no proof of 
this. They do not appear to be fossiliferous. Some of the gravels 
contain fossils, but these fossils belong to the original formations 
from which the pebbles were derived. 
COLUMBIA SANDS. 
Overlying the Lafayette beds there is a heavy deposit of gravel, 1 he 
age of which has not yet been definitely determined. By some it has 
