STRATIGRAPHICAL GEOLOGY 
425 
In the rush of myriads of other things thrust upon the Survey 
the immediate cause for the disappearance of the Cretacic beds 
north of Red Oak did not occasion any especial interest. It was 
long years afterwards that the basic reason was found. On the 
Missouri River to the westward a disturbance of strata was long 
known but it was regarded as a fold; but close examination soon 
disclosed that it was really a fault of considerable throw — about 
300 feet. As the dislocation line passed across Montgomery 
County north of Red Oak it had the Cretacic sandstones on the 
one side and the Carbonic shales on the other. The Cretacic form¬ 
ation to the south escaped obliteration in the general planation of 
the region by having been dropped beneath the level of regional 
denudation. 
A wide belt of country north of the Red Oak fault-line is there¬ 
fore properly to be mapped as Carbonic instead of Cretacic. This 
broad belt, bordered on both sides by Cretacic formations, extends 
from beyond the Missouri River northeastward into central Iowa, 
and completely bisects the Cretacic area. The long southern pro¬ 
truding tongues of Dakotan sandstone which occupy the inter¬ 
stream uplands are therefore Cretacic outliers in place of ap¬ 
panages of the main body of the Mesozoic tract. 
Ke:ye:s. 
Rio Grande Carbonic Province. For three distinctive reasons 
the Rio Grande province of Carbonic rocks recently excites great 
interest; and assumes an important place in the consideration of 
later Paleozoic stratigraphy. First, through the Rio Grande se¬ 
quence of strata the Carbonic formations of the Great Basin 
region of western America are readily harmonized with the ter- 
ranes comprising the Standard American section, as represented in 
the Mississippi Valley. Second, the Rio Grande section of Car¬ 
bonic rocks is the most complete and the most extensive succession 
of this age on the whole American continent. Third, a great 
thickness of beds, nearly 4,000 feet, appear to represent Paleozoic 
deposition much younger than any other known in America, and 
perhaps in the world. 
In a recent review of the widely scattered and indifferent litera¬ 
ture on the ore deposits of New Mexico there are prefaced sketch¬ 
es of the geologic features of the region. The Carbonic succes- 
