108 The American Geologist. August, 1892 
ward; the Texan and Great Plains regions, with much of the present 
Rocky mountain region, were covered with 2,000 feet of sediment. 
The remnantal outcrop of this great formation is shown upon 
the maps. Its sediments record the sequence of events as the 
Lower Cretaceous; that is (1) basement littoral beds of sand, (2) 
deeper beds of clay, calcareous in their apper portion, (3) a deepest 
stage of almost pure chalks, (4) beds shallowing towards the top. 
How much of the Comanche series was destroyed by base- 
leveling during this epoch can only be surmised. 
At the close of the Upper Cretaceous the most marked uplift 
of the Rocky mountain region took place, and the ocean's waters 
again receded nearly to their present outline. Again land degra- 
dation and deposition began, resulting in the third loading down 
of the coastal plain, followed by the cycle o^ deposition and sub- 
sidence of the Eocene epoch. 
During the basal Eocene the central Texan region was covered; 
how far and to what extent is problematical, but another heavy 
load was added to the coastal plain. 
The great hiatus in the geologic history of the region is of 
Neo-Pliocene time, between the close of the Eocene and the 
beginning of the Appomattox. The present state of ignorance 
allows but little to be said of it. 
It is not known whether at the close of the Eocene there was 
any important event, such as the elevation or subsidence of the 
coastal plain. We have knowledge of only the basement history 
of the marine Eocene. Its upper contacts or gradation have 
never been studied or presented. 
It is known, however, that in Miocene or Pliocene time an- 
other shore line had developed along the Rocky mountain front, 
into which flowed the drainage of the Rocky mountain region, 
and all the vast region between the Rocky mountains and the 
coast was once more laden with sediments, and later these plains 
were elevated into the dry land which they have since remained; 
the}- present a vast sheet of sediments upon much of which 
drainage channels have not yet been established, but so degraded 
and eroded upon its eastern edge, that their former extent in that 
direction has not been determined. No portion of the geologic 
record is more obscure than that of the conditions of the coastal 
region during this Mio-Pliocene epoch. Whether the Llano 
Estacado formation, which now covers and is co-extensive with 
the Great Plains region, was laid down at marine or lacustral base 
