118 CRETACEOUS ROCKS OF TEXAS. 



manche 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 re- 

 gion, 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, grad- 

 ating 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 arena- 

 ceous in composition, clastic in structure, and composed at its base of con- 

 glomerates 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 postoflice, 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 Triqonias, Pholadomyas, Cyrenas, and an undescribed 

 Ammonite resembling Hoplites dispwr. 



