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rocks, schists, limestones, sandstones, and pre-Trinity granites. Succeeding the basal conglomerates are coarse, angular, cross-bedded sand, becoming finer and finer until it reaches the fine condition known in Texas as "pack sands," i. e., a 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 consisting of indeterminate Trigonias, Pholadomyas, Cyrenas, and an undescribed Ammonite resembling Hoplites dispar. In this vicinity, also, appears the first of the several conspicuous Grypheate beds of the Comanche series. This is composed of a solidified mass of large Grypheate oyster shells resembling the dilate species figured by Marcou as Gryphæ dilata, but not yet positively determined. These were found to form a breccia seven or eight feet in thickness, just below the crossing of the Travis Peak and Nameless road. Accompanying the Gryphæa breccia there is also the first appearance of another conspicuous feature in the Comanche series, i. e., an excess of magnesian sulphate. The oyster shells are being rapidly cemented into massive limestone beds or decomposing into a powdered earthy substance accompanied by incrustations of Epsom salts (Epsomite). This magnesian feature, which becomes more conspicuous higher in the series, is a fine illustration of an instance of the conversion of a shell limestone into dolomite by an alteration subsequent to the formation of the original rock, as has been recorded by Irish geologists.

In places throughout the sands are occasional patches of red and greenish white clays resembling very much the characteristic features of the red beds of the lower formations. The cause of these discolorations has not been studied. There are about 300 feet of these arenaceous Trinity beds in the Colorado section, at the top of which appears a fossiliferous horizon-the first or lowest appearance of Monopleura and Requienia (Caprotina)-which we assume to be the beginning of the second division of the Comanche series. Thus the Trinity beds in the Colorado section are seen to be composed of locally derived debris, which, as the waters deepened, became more and more comminuted and calcareous until the sand grains at the top are almost imperceptible to the eye, and the whole mass becomes quite chalky and magnesian in appearance. As shown elsewhere, these basal arenaceous beds everywhere vary with the shore line upon which they were laid down, and are entirely different in the Brazos and Arkansas sections. (See Hill 1 and 4.)

The Caprotina horizon No. 1, which, according to our classification, lies at the "

See Prestwich's "Geology, Chemical, Physical, and Stratigraphical," Vol. 1, pp. 113, 114.