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Cretaceous seldom contain more than 50 per cent of calcium carbonate, the average being 20 to 40 per cent.

The "white rock," or Austin chalk, abounds in fossils, most of which, however, are but poorly preserved casts.

The economic advantages of the "white rock," or Austin chalk, are various. It affords good locations for the building of cities and communities, not only on account of the firm foundation for building and road beds and good drainage which it always affords, but on account of its sanitary conditions, produced by the imbibing capacity of the chalk. When accurate statistics are kept, it will be proved that dwellers upon the chalky lands have a great hygienic advantage over those upon sands and clays. The chalks are also water bearing, and while yielding their moisture slowly, they afford an abundance for domestic purposes, and play an important part in the transmission of the rainfall to depths from which it can be abstracted, perhaps, in East Texas, by artesian wells. The chalk is also valuable for the manufacture of whiting, rouge, etc. Chalk is most used in England, however, where scientific agriculture has attained its highest development, for dressing lands. Thousands of tons are used annually on the non-calcareous lands of England, where it is usually applied at the rate of twenty tons per acre, just as it will ultimately be used upon the non-calcareous lands of East Texas, as soon as our agriculture advances to a stage where its necessity will be appreciated. Chalk makes a cheap, convenient land dressing for non-chalky lands, performing in a more satisfactory manner the functions of quick-lime in making available other constituents of the soil and humus, besides contributing to it minute but valuable proportions of phosphates, potash, and other plant foods.

The chalk will also prove of great use in the manufacture of Portland cements. Chalk is the material used in the manufacture of most of the imported cement, and when the people of our State properly appreciate what an immense industry lies at their doors—a natural Texas monopoly—this region will become a great cement center for the United States.

The eastward continuation of the Austin-Dallas chalk is covered by what "

The most characteristic species are Hemiaster texanus, Rœmer, Ammonites (Mortoniceras)texanus, Rœmer, Terebratella guadalupe, Rœmer, and Ammonites dentato-carinatus, Rœmer. The most abundant fossils, however, are genera which range upward into the Ponderosa marls, including the numerous moulds of Inocerami and great masses of the young forms of Exogyra ponderosa, Rœmer. Baculites, Pecten, and many other Upper Cretaceous species are plentiful.

The name given these marls is taken from the large fossil oyster, called Exogyra ponderosa by Dr. Rœmer, which occurs in immense quantities in certain beds.