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These clays cover an extensive area, being found in a well near Forest, in Cherokee county, and at Crockett, Houston county, where they are exposed on the surface of the ground and in creek cuttings over a width of from three to four miles of country, and are also found in Wells near Paso and Lovelady. They are also exposed at Alabama Bluff on the Trinity river where they cross into Leon county. In the bluff these clays rest upon the same fossiliferous brown sands as in Collin's branch and other exposures around Crockett. The same clays are exposed on the Houston, East and West Texas railway, near the Angelina river in Angelina county, and'extend southward to the foot of the gray sand ridge in Polk county two miles south of the Neches river. The same clays are again seen about a mile east of Corrigan, where they pass under the soft white diatomaceous earths belonging to the sandstone belt. The exact area of these deposits is not known, but so far as the present investigation goes, they appear to occupy a belt of country about twenty-five miles wide and to have a thickness of thirty feet.
The extensive lignite deposits of western and southeastern Houston and northern Trinity counties are found in the region occupied by these clays.
Owing to the total break in the character of the material between these clays and the underlying fossiliferous greensands and iron deposits, these beds have been tentatively assigned to the Miocene division. They may, however, upon further examination be placed in an intermediate group, and may probably be found to be representative of the Oligocene beds.
EOCENE.
Immediately underlying the Miocene deposits, and closely connected with them by the series of laminated sands and clays and gypseous massive clays and sands already mentioned, comes the older Tertiary deposits of the Eocene. These deposits have here been given a thickness of about 1500 feet, and have been divided into an upper and lower division, corresponding very nearly to Dr. Penrose's Timber Belt beds and Basal clays.
All or nearly all of Penrose's Timber Belt beds have been assigned to the upper division of the Eocene.
The general facies of these beds are iron ores, mostly clay ironstone or carbonate of iron and some laminated iron ore, thinly stratified fossiliferous and unfossiliferous ferruginous sandstones and sands, fossiliferous and unfossiliferous altered and unaltered greensands, green and black fossiliferous clays, green and blue fossiliferous marls, thinly laminated clays and sands, with occasional deposits of lignite, the fossiliferous greensand beds predominating everywhere throughout the area.
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Areally these deposits occupy a broad stretch of country, the line of the section passing over them from near Edgewood station, in Van Zandt county, where they overlie the lower deposits, to the northern edge of the Miocene deposits in Cherokee county, a direct distance of about 110 miles. The exact lines of contact between the overlying Miocene as well as the lower Eocene, or Basal clays, have not been accurately determined, nor, from the sections as yet seen, does it appear possible to do so. At the base of the Miocene deposits and on the top of the Eocene there lies a series of thinly laminated blue clays and sands containing numerous crystals of selenite and gypsum. These have for the present been assigned to the Miocene, but some of them may ultimately be found to belong to the underlying Eocene. On the other side, or at the base of the' Eocene marl beds, the upper beds of the lower Eocene grades up into the sands lying at the base of the upper division. The change is so gradual that in the absence of fossils it is almost impossible to determine the exact limits of each. The places assigned to these different beds, however, will not vary more than a few hundred yards in surface exposure in either direction.
Structurally these deposits show a peculiarity which has not as yet been noticed in any of the overlying deposits. While the general slope of the whole country is southeasterly at a small dip, many of these beds dip towards the northwest for short distances, and at other places give sections showing a horizontal disposition or present condition. These changing dips give the beds an undulatory appearance, although in nearly every instance observed erosion had completely cut off the upper folds of the beds, and in many places the apex is now worn so far down as to be occupied by a stream bed. There is nothing, however, in connection with these changes of dip to indicate that this undulation is due to any extraordinary means or anything more than the effects of the erosion of the underlying sands. This flexing or bending of these beds disappears near the southern limit of the area occupied by them, and they then present a long, gentle slope, not exceeding 16 feet per mile, towards the southeast.
While some of the deposits may be looked upon as not fossiliferous, or at least containing a very scanty fauna, the southern margin, both in Cherokee and Houston counties, is remarkably rich in fossil shells, fish teeth and small corals, and in Houston county particularly so. In the streams and washouts crossing Murchison prairie, in the northeastern portion of this county, Cardita, Cerithium Whiffieldi, Natica and several varieties of oyster can be obtained in great profusion. The oyster bed overlies the deposits containing the other fossils and is usually a brown sand. The underlying fossiliferous bed is a bluish green marl, stained brown upon the upper surface, and is frequently separated from the overlying brown sands by a deposit of phosphatic nodules. These nodules are very irregularly deposited, and so far as seen not more than