114 CRETACEOUS ROCKS OF TEXAS. 



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 vari- 

 ous. 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 .condi- 

 tions, produced by the imbibing capacity of the chalk. When accurate sta- 

 tistics 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 trans- 

 mission 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 manu- 

 facture 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 appre- 

 ciated. 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 contribut- 

 ing 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 im- 

 ported 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. 



NO. 4. THE EXOGYRA PONDEROSA MARLS. f 



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



*The most characteristic species are Hemiaster texanus, Rcemer, Ammonites (Mortoniceras) 

 texanus, Roemer, Terebratella guadalupoe, Roemer, and Ammonites dentato-carinatus, Rcemer. 

 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, Roemer. Baculites, Pecten, and many other Upper Cretaceous 

 species are plentiful. 



f The name given these marls is taken from the large fossil oyster, called Exogyra pon- 

 derosa by Dr. Rcemer, which occurs in immense quantities in certain beds. 



