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According to Professor Fontaine, the plants found at Glen Rose show, so far as can be judged from so imperfect a collection, that the Trinity flora finds its nearest analogue in the older portion of the lower Potomac. There is, however, this important difference: No trace of angiosperms, even the most archaic, has been found. We have only the four elements of the typical Jurassic flora. This, then, makes the Trinity flora somewhat older than that of the oldest Potomac. The absence of the angiosperms and the presence of the forms that are found, indicate decidedly that the Trinity flora is not younger than the earliest stage of the Cretaceous.
PALUXY FORMATION.
CHARACTER AND OCCURRENCE.
The Paluxy sands (see Pls. LXVI and LXX), although of less areal extent than the lower sand beds, mark an important horizon, inasmuch as they are a valuable source of artesian water in the region of their embed and of surface wells in the area of their outcrop.
In Wise, Parker, Hood, Erath, Somervell, Bosque, Hamilton and Coryell counties the Glen Rose limestones grade up into a well-defined and mappable formation, which attains a maximum thickness of 100 feet, composed of fine white packsands closely resembling the Basement sands, of which they are a ramification, as is elsewhere shown, and the outcrop of which corresponds to the eastern limbs of the Western Cross Timbers, as shown on Pl. LXVI. When these sands outcrop on slopes or plains, or otherwise than in vertical exposures, they are marked by a growth of forest timber, largely post oak and black-jack.
As a whole, the Paluxy bed is a body of homogeneous, fine-grained, porous, compact, but not indurated sand, bearing numerous specimens of silicified and lignitized wood. In detail it is false bedded on an extensive scale, and often finely and beautifully laminated. Lenticular bands of impure clay occur, with lignitic sand in like form. The basal position of the sand becomes calcareous and flags of compact semicrystalline shell limestone sometimes occur in the marly sand. Near its upper limit the sand becomes argillaceous in some localities, and occasionally there are nearly pure clays. The sand is stratified "
Op. cit., p. 279.