181)3.] NATURAL SCIENCES OF PHILADELPHIA. 321 



perhaps the best example of a newly born topographic plain in this 

 country." Of the same region Penrose says 18 "the coast prairies 

 reach inland along the Sabine about fifty miles, but as we go west 

 they spread farther and farther toward the interior, until when we 

 come to the Brazos, they reach up the river for over a hundred 

 miles. Near the Gulf shore they are flat and low, rising twenty to 

 thirty feet above the water, thickly covered with grass and cut by 

 steep-sided channels of many rivers and creeks. The monotony of 

 the scenery is broken only by the narrow strips of timber which fol- 

 low the meandering course of the streams down toward the Gulf of 

 Mexico. " On its inner or western margin it becomes undulating 

 and merges into the rolling timber area. 



Where I crossed the plain from Houston to Galveston it is little 

 more than an undrained swamp. The steep-sided stream channels 

 are sunk but a few feet beneath the surface and between these are 

 great flat-topped, undrained divides upon which water stands dur- 

 ing the greater part of the year. Rushes and swamp grass have 

 possession and even cattle find the plain too inhospitable for habita- 

 tion. Now and then, though very rarely even along the railroad, 

 on some slight elevation a settler has placed his house and a few cat- 

 tle graze in the vicinity. Everywhere else there is one monotonous 

 stretch of dead-level plain. So young is the plain that recent fossils 

 at present living in the Gulf are preserved in the prairie strata. 



(b) Young, Consequent, and Extended Drainage. — Two types of 

 rivers exist upon this coastal plain : the extended rivers, having 

 their supply in the interior, and the young consequent streams which 

 are developing between these. The Brazos, Colorado and Trinity 

 are instances of the former and innumerable creeks are examples of 

 the latter. 



The extended rivers, receiving their supply of water and sediment 

 from the inland plains, reach the Quaternary prairies as full sized, 

 well developed streams and they monopolize the drainage of the 

 plain. As the plain was elevated they grew out across it and 

 by their power, resulting from size and priority of location, they 

 have seized upon the major part of the plain as their own. The 

 extended course is consecpient on the original slope of the plain; 

 that is, Gulf-ward. In the spaces left undrained by these larger and 

 stronger rivers consequent streams are hoav developing. The 

 extended streams grow at their mouth, the smaller young streams 



'"First Am. Kept., Texas Geol. Survey, 1889, p. 7. 



