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series consist of from 1000 to 2000 feet or more of predominatingly calcareous (chalky) rocks, sometimes argillaceous and arenaceous, as shown in the section beyond, arranged in almost horizontal layers, of varying degrees of hardness, and great uniformity in extent. They usually incline coastward; in places are considerably jointed and faulted. Its rocks, like those of the Upper series, from bottom to top record a complete ternary succession of strata, to-wit: 1. A lower stage of sandstones, shales, and other sedimentary deposits, representing prevalence of land with downward movement. 2. A middle stage, chiefly of limestone, representing prevalence of sea, and general quiescence and elaboration of calcareous organic formations. 3. An upper stage, and more of mechanical sediments, indicative of proximity to land.
The whole Comanche series is thus divided into three grand divisions, to-wit, the Trinity or Basal (sandy beds), the Fredericksburg or Medial (chiefly chalky beds), and the Washita or Upper division (impurer chalks and clays, alternating in stratification, becoming slightly arenaceous in the Denison region, but not so at Austin, for reasons explained later).
NO. 1. THE TRINITY SANDS OR UPPER CROSS TIMBERS DIVISION.
TRAVIS PEAK SANDS, OR WATER-BEARING BEDS.
In every place where the base of the Comanche series has been seen it has had the coarse sedimental characteristics of a near-shore formation, gradating upward into finer and deeper sea deposits. The eastern edge of the Upper Cross Timbers is a good illustration of the beds. In the Colorado section, near the Burnet-Travis county line, this division is essentially arenaceous in composition, clastic in structure, and composed at its base of conglomerates or sands, the origin of every pebble of which can be located in the adjacent and more ancient strata of the Paleozoic region. In the south- eastern edge of Burnet county the Trinity sands are in contact with the Paleozoic schists, limestones, sandstones, and pre-Trinity granites. Succeed- ing the basal conglomerates is a coarse, angular, cross-bedded sand, which becomes finer and finer until it reaches the condition known in Texas as "pack sand," i. e., a very fine grained sand, which is cemented by included chemically precipitated calcium carbonate. Fossils have been found by the writer at Sycamore Creek, Burnet County, in the contact conglomerates, but they are neither plentiful nor distinct until the upper or pack sand beds are reached, one mile below Travis Peak postoffice, where the arenaceous layers are full of casts and moulds.
In this vicinity, also, appears the first of the several conspicuous oyster"
These consist of undetermined Trigonias, Pholadomyas, Cyrenas, and an undescribedAmmonite resembling Hoplites dispar.