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The economic aspects of the Comanche Peak beds are mostly æsthetic. Their weathering adds beauty to the landscape, and the remnants of ancient marine life so abundantly preserved in it should afford abundant material for instruction to those who are capable of appreciating the grander features of the earth's history. The chalks, were they the only ones in our State, would perhaps be of great economic value for cement making and agricultural uses, and the remarks applied to the Austin chalk, on page 114, are equally applicable to them.

Without any observed stratigraphic break, the Comanche Peak chalk gradates into 300 feet, more or less, of chalks and chalky limestones of varying degrees of consistency, from a pulverulent condition to firm limestones, which seem to be a secondary condition of the chalk produced by superficial hardening. These hard layers form the cap-rock of the buttes and mesas or highlands of the extensive Grand Prairie region, and are the cause of the flat topped topography of the so called mountains of Central Texas. They usually occur at an altitude above 1000 feet along the margins of their eastern outcrop, but at Austin they have been broken along the line of their strike by a great fault, and as a result the eastern side has fallen down from 1500 to 750 feet above sea level, as exposed in the river bluffs between Austin and Mount Bonnell, on the Colorado, where the chalk has been more or less hardened into firm limestones by the local metamophism accompanying faulting.

In these chalks and chalky limestones are well defined layers of exquisite flint nodules, occupying apparently persistent horizons in localities. These flint nodules are oval and kidney-shaped, ranging in size from that of a walnut to about two feet in diameter. Exteriorly they are chalky white, resembling in general character the flint nodules of the English chalk cliffs. Interiorly they are of various shades of color, from light opalescent to black, sometimes showing a banded structure. These flint nodules are beautifully displayed in situ in the Deep Eddy canyon of the Colorado, above Austin, where they can be seen occupying three distinct belts in the white chalky limestones.

Where these chalky limestones form the mesas of rapidly weathering plateaus, such as the remnants of the Grand Prairie west and southwest of Austin, the flints are left in great quantities as a residuum (the softer chalks being more readily decomposed into soils and washed away), and they cover large areas of country. They have also been transported eastward in past geologic times by marine and river action, and are distributed over large areas along the margin of the Black Prairie region as a part of the Post-Cretaceous