1 1 4 The American Geologist. August, 1892 
In the Neozoic series, however, there are but three formations 
sufflcieutl}" consolidated to produce canoned or scarp topography 
— the iron ore beds of the Eocene, certain white rock beds of the 
Miocene or Llano Estacado, the Fayette beds, and the limestones 
of the Comanche series. 
The first two — the Eocene iron beds of east Texas and the 
Miocene beds of the Staked Plains — are thin horizontal beds of 
consolidated material underlaid by loose friable beds which rapidly 
disintegrate upon the removal of the cap sheet and produce mesas. 
These mesa prodi^cts are not greatly developed in East Texas 
because of the newness of the streams, but in the Llano Estacado 
are verj- marked. 
The great chalky limestone formation of the Comanche series 
has been the chief factor of resistance to sculpture in the Texas 
region, and the effects produced by erosion of its alternations of 
hard and soft beds are both beautiful and instructive. Along 
its eastern margin where it dips beneath the Upper Cretaceous its 
prevalent forms are dip plains and escarpments of stratification 
extending north and south; many streams flow along them in the 
same directions until they cut their way through the escarpment, 
when they again flow eastward to the sea. In the west central 
portion of the state headwater erosion of opposing streams has 
produced numerous buttes and mesas, which are often a hundred 
miles from the mother area of which they were a part. 
While the general coastward direction of the streams is the 
result of the prevalent slope, there are certain influential struc- 
tural features which in the aggregate produce the prevalent topo- 
graphic detail. 
First of these are joints and faults. 
The stratigraphic system of this region is broken by a S3'stem 
of complemental joints which have a major axis of west of south 
to east of north or sub-parallel to the coast line. In areas of 
unconsolidated chalks, sands, and clays, joints have no percepti- 
ble etfect in deflecting streams, but where the material is consoli- 
dated streams adapt their courses to joint lines; this is shown by 
the Brazos in the Carboniferous rocks of Palo Pinto count}", the 
Colorado in the Lower Cretaceous of Travis, and in other 
instances. 
