XXX REPORT OF THE STATE GEOLOGIST. 



cut here and there by canyons, formed by the encroaching action of 

 the headwaters of the Colorado, Brazos, and Eed rivers. 



The fourth district comprises that portion of the country beyond 

 the Pecos Eiver, which is a part of the Eocky Mountains themselves, 

 crossing the western border of the State, as they trend from New 

 Mexico, and find their continuation in the rich mineral districts of the 

 Mexican Eepublic. Here there are real mountains, which lift their 

 peaks from 6000 to 8000 feet above the waters of the Gulf, often rising 

 directly from the surrounding comparatively level plains, or flats of 

 lake deposit, which enclose them on every side. These so mask the 

 real relations existing between the ranges, and even between individ- 

 ual peaks of a range, as to render the accurate determination of their 

 connection with each other a matter of considerable difficulty. Thus 

 it is that we have within our borders most of the phases of American 

 geology, and indeed some conditions which have not been hitherto 

 observed on this continent, and which resemble more nearly those of 

 Europe. 



Not only is it true that we have here representatives of all these 

 different formations, but their areal distribution is on a scale commen- 

 surate with Texan greatness. Comprising, as Texas does, one-twelfth 

 of the area of the United States, some of her single formations cover a 

 larger area than is found within the entire borders of some of the sin- 

 gle States, and those by no means the smallest. Taking these facts 

 into consideration, the amount of labor before us can be more readily 

 understood, and the results here given be more nearly appreciated at 

 their proper value. 



Geologists divide the various strata or layers which go to make up 

 the crust of the earth, as we know it, into four main groups. This 

 division is based upon the character of the fossil remains which are 

 found preserved in each separate group, and which show the progress 

 of life in the history of our globe. From long continued observations 

 of the positions and relations of the various beds, layers, or strata to 

 one another, and the constancy of the occurrence of certain fossil forms 

 of animal or vegetable life in each ai a definite horizon, the order of 

 succession has been made out. These general groups have in turn 

 been subdivided. Each of these formations is usually accompanied by 

 certain articles of economic importance, which are the results of the 

 manner of their deposition, or of alterations which have taken place 



