Geographic Features of the Texas Region. — Hill. 69 
This valley is from twenty to sixty miles in width, and about 
800 feet below the level of the plain. It transects its entire 
width from the 100th to the 105th meridian. Its walls, espec- 
ially the south one, are very steep and apparently perpendicular 
when viewed from below, forming a grand and beautiful feature 
in the landscape. The bottom of the valley is but slightly con- 
cave, almost a plain itself, and covered with an extensive 
detrital formation of calcareous pan, accompanied by siliceous 
pebbles, much worn and rounded. For this formation I have 
proposed the name Terra-Blanca, used by the Mexican inhab- 
itants of the valley. 
Within this valley and running through it is developed the 
modern drainage system of the Canadian, a mere pin-scratch 
in proportion to the larger chasm. This cuts through the 
Terra-Blanca formation into the Red Beds and its flood-plain 
has the general aspect of the drainage of the Red Bed region. 
The Canadian of to-day, with its laterals, is newer and subse- 
quent to the ancient valley. The writer has traversed only 
two hundred miles of this valley, and then so hastily that he 
must leave it to others to work out its detailed structure and 
history. The investigator who will take up the study of this 
ancient chasm, and ascertain its origin and that of the Terra- 
Blanqa formation which fills it, will find in it the key to the 
later geologic history of the western United States. 
The Older Valley of Red river. 
A somewhat analogous valley to that of the Canadian is to 
be found on the Indian Territory side of Red river between the 
98th and 96th meridians, as transected by the IMissouri, Kan- 
sas and Texas and the Atchison, Topeka and Santa Fe rail- 
ways. Here the modern Red river flows through an ancient 
alluvial deposit of from twenty to forty miles in width, filled 
mostly with the debris of the Red Beds, and far above the 
altitude of the present stream. Too little is known of this 
valley to discuss it here, except to say that its direction sug- 
gests a continuation with the Canadian valley on the west and 
the Little Missouri valley on the east. Nearly all of the Grand 
Prairie north of Red river has been destroyed by this erosion. 
THE RIVER TERRACES OF THE BLACK PRAIRIE AND EO-LIGNITIC 
REGIONS. 
All the rivers of the first class occupy wide and deeply ter- 
