110 The American Geologist. xvugust, isgj 
During the culmination of the Appomattox a third and distinct 
system of drainage was evolved along the then low lying coastal 
plain, adjacent to and interior of its shore line. This group of 
rivers is easily traced upon the maps and includes the San Gabriel, 
Lampassas, Leon, the Bosques, Paluxies and Trinities. They 
are short streams not exceeding 100 miles in length, and drain 
the ancient structural or dip plain of the Grand Prairie, or Lower 
Cretaceous region. Their profile in relation to the plains which 
they drained are as shown upon the diagram, and they are rela- 
tively 500 feet higher at their heads than the adjacent and more 
deeply cut drainage of the first and second systems. The de- 
bouchement of these streams during Appomattox time is clearly 
marked upon the map by the great estuarian deposits, as shown 
by the river terraces especially of the Colorado where it emerges 
from the canons of the Grand Prairie (Appomattox land) into the 
Black Prairie (Columbian coastal plain). The sea receded and 
the submerged plain of Appomattox became dry land. The sea 
shore reached about one-half the distance between the present 
coast line and the ancient Appomattox shore. This was the 
Columbian epoch of Pleistocene time. Upon the new land, the 
present coast prairies, still a fourth system of coastal drainage, 
was initiated almost similar in extent and aspect to that of 
Appomattox time. The rivers of the third or Appomattox sys- 
tem were extended to the Columbian shore, while those of the 
second or Colorado, Brazos, pre-Appomattox type became long 
estuaries back to the Appomattox shore line ; at the close of that 
period change in the direction of slope caused them to form a 
line of junction with some adjacent stream, either with one of 
the older streams or with one another. These streams were ac- 
celerated by the elevation at the close of the Appomattox and 
Colorado, and have since cut deeper but proportionately less 
channels than the more voluminous streams of the older systems. 
Few of these streams have crossed by headwater erosion the 
great western scarp of the Grand Prairie ; at present this portion 
of their development seems retarded for where they have crossed 
the western scarp line it has been by capture — by the laterals of 
the older streams. 
The Columbian deposition plain, the present coastal prairie, in 
turn became dry land by the recedence of the gulf to its approx- 
imate present coast line; upon this recentl}^ submerged area was 
