1XXX REPORT OF THE STATE GEOLOGIST. 



Mountain, Cherokee County, but such are unusual south of the Grand 

 Prairie. This character of country is continuous from the Gulf to the 

 western scarp of the Grand Prairie, east of the Brazos Kiver. West of 

 the Colorado Eiver the undulating country ends at the foot of the 

 southern scarp of the Grand Prairie, which is a line of elevations known 

 as the Balcones, from the top of which the Grand Prairie stretches away 

 north and west to the Rio Grande. The eastern portion of these belts 

 is heavily timbered, but throughout the greater portion — west of the 

 96th meridian — the quantity of timber rapidly decreases and the prairie 

 conditions become almost universal. The general elevation east and 

 south of the Grand Prairie is less than five hundred feet. 



The Grand Prairie itself is a great plateau, preserved in its present 

 extent by the resistence to erosion afforded by its capping of limestones, 

 and is a marked topographic feature of the State. Beginning at Red 

 River it extends in a gradually widening belt to the south, until its 

 western border meets the Colorado in Lampasas County, from which 

 point it is contracted rapidly until it finds its narrowest exposure in 

 crossing the river in Travis County north of Austin. From this point 

 west it broadens rapidly, until it is merged into the mountainous Trans- 

 Pecus region. Its height above the country on either side is variable. 

 On its eastern border, from Red River to the Brazos, there is not that 

 abruptness of separation which distinguishes it at other places from the 

 upper and lower formations. In the northern portion this plateau be- 

 gins with an elevation of from six hundred to twelve hundred feet 

 above sea level. West of the Colorado its northern edge reaches a 

 height of twenty-three hundred feet in the ridge which forms the divide 

 between the water flowing into the Colorado and that flowing south. 

 The southern border is, however, hardly ever more than seven hundred 

 feet in height, and usually not so high. The western and northern 

 edge of the Grand Prairie is, generally speaking, topographically higher 

 than the eastern and southern, and the dip of the beds is very gentle 

 toward the southeast. 



The break between the Grand Prairie and the Central Basin region 

 is equally as decided as that between the undulating country and "Bal- 

 cone's country " on the south, and were it not for its intimate relations, 

 geologically, with the Coastal Slope, the topographic features of the 

 Grand Prairie would entitle it to be considered a division by itself. 



Both topographically and geologically this area presents a gradual fall 

 from the interior toward the Gulf coast, but the average slope of the 



