22 OIL FIELDS OF TEXAS-LOUISIANA COASTAL PLAIN, [bull. 212. 
The rapid changes of texture of these beds from sands to sandstones 
and again to sands may account for the difficulty of recognizing the 
Fayette sands in the boring of the wells around Spindletop, and it is 
possible, though improbable, that some of the thin-bedded irregularly 
deposited sandstones reported belong to these beds. 
In connection with the Fayette sands a comparatively heavy bed of 
thinly laminated brown and gray clays, carrying considerable quanti- 
ties of iron pyrites, is often found, and a considerable amount of 
sulphur is disseminated through them. These clays first make their 
appearance on the Brazos River, and occur on the Colorado and on 
Elm Creek near Muldoon in Fayette County. They also occur in 
Starr County on the Rio Grande. They do not appear on the Trinity, 
and their extent east of the Brazos is unknown, as no exposures are 
found. They appear to lie in a long, narrow trough and to be from 
10 to 50 feet in thickness. In Faj^ette County they are associated 
with small quantities of petroleum, and It is possible that they are the 
source of the small seeps of oil found in the overlying sandstones in 
Waller County. 
FRIO CLAVS. 
The geologic horizon of the succeeding Frio clays a is not so clear 
as in the case of the Fayette sands, on account of the enormous 
amount of erosion that must have taken place between their deposi- 
tion and that of the next succeeding formation, and on account of 
the great extent to which the Frio clays are overlapped by later 
formations. 
The character of the Frio cla3 r s is more persistent than that of the 
Fayette. A heavy deposit of blue clay with its conspicuous line of 
calcareous nodules forms a horizon as prominent and well marked as 
the most continuous ledge of sandstone in the Fayette. The other 
clays of the Frio are not so uniform either in thickness, texture, or 
continuity. While they generally contain carbonate of lime, at some 
places this lime is replaced by gypsum, and the clays themselves by 
sands. The Frio beds appear to have been found in the Federal Crude 
well at Beaumont at a depth of 2,300 feet. From the nearest outcrops 
of these clays to the well the distance is about 75 miles. This would 
give the beds an approximate dip of 35 feet per mile. The Frio clays 
have not as yet been recognized in the logs of any wells producing 
petroleum. From west to east the Frio clays change considerably in 
«In the Third Annual Report of the Texas geological survey the Frio clays were described 
under the name of the Fleming beds. Later, Dumble, working on the Frio River, found the 
same beds well developed and suggested the name Frio clays, which was adopted, and these 
clays have been known as Frio clays ever since. Quite recently Mr. A. C. Veatch examined the 
same clays in the vicinity of Burkeville, Newton County, Tex., and in his report suggests the 
name "Burkeville beds" for them. The writer, having examined the whole series from their 
exposures on the Frio River eastward through Texas, including the exposures at Fleming, near 
Jasper and Burkeville, and across the Sabine as far as the line of the Kansas City Southern Rail- 
way in Louisiana, and finding these clays the same in each place, considers that the name Frio 
clays should be retained, and that it is unnecessary to introduce the name "Burkeville beds,' 1 at 
least into the nomenclature of the Texas areas.— W. C. 
