. The geography of Texas, physical and political. of this change may be mentioned thehardening of some sandstones into a rock called quaitzite^or the alteration of ordinary limestone into marble. Some altered rocks break easily in the direction of theirbedding, — the minerals of which they are composed arearranged in bands or layers. Such rocks are termed break into thin plates across their bedding. Theyare slates. 12. The Rocks of Texas. With the exception of a smallarea known as the Burnet country, or Central Mineralregion, all of Texas east of the Staked plains, as well asthe
. The geography of Texas, physical and political. of this change may be mentioned thehardening of some sandstones into a rock called quaitzite^or the alteration of ordinary limestone into marble. Some altered rocks break easily in the direction of theirbedding, — the minerals of which they are composed arearranged in bands or layers. Such rocks are termed break into thin plates across their bedding. Theyare slates. 12. The Rocks of Texas. With the exception of a smallarea known as the Burnet country, or Central Mineralregion, all of Texas east of the Staked plains, as well asthe region of the Edwards and Stockton plateaus, is under-lain by rocks of marme origin, that is, by sea deposits. TheStaked plains, however, are capped by nonmarme deposits. In the Trans-Pecos region of mountains and basins thereare found not only marine and nonmarine deposits butalso igneous and altered rocks. GEOLOGY 13. The Geological Map. The various rock systems^arranged in the order of their age, the youngest or latest GEOLOGICAL MAP TEXAS. H ^ Eocen. G 1> g^ Carbonirerous I 1 Dttoiiiau and f Not Reprmenttd t- I ISilniUi. I inlheStaw a OrdovLUn and ? Camhnai AtjItVj Aiifflif Fig. 2 formed at the top and the oldest at the bottom, are asfollows; 9. SiUiriaii.^ 10. Ordovician. 11. Cambrian. 12. Archaean (bottom). Their distribution in Texas is shown on the accompany-ing geological map. It will be seen that the}^ outcrop, for 1 At present not known in the state. 1. Recent (top) 2. Xeocene. o. Eocene. 4. Cretaceous. 5. Jura-Trias. 6. Permian. 7. Carboniferous. 8. Devonian.^ 10 THE (;eo(;rapiiy of texas the most part, in a series of more or less parallel belts orstrips running in a northeast and southwest , until the Staked plains are reached, each belt,beginning with that bordering the (lulf of Mexico, is of agreater age than the preceding. The rocks of the liuriiet
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