IOWA ACADEMY OF SCIENCE 
159 
CARBONIC COLUMN OP RIO GRANDE REGION. 
BY CHARLES E. KEYES. 
The character of the later Paleozoic succession in southwestern United States 
has radically modified our general ideas regarding carbonic history in America. 
As directly bearing upon this subject the Carbonic rocks of the New Mexican 
region are of exceptional interest. The Rio Grande section, if it may be so 
designated, is serially the most complete in the country. It is of great thick- 
ness. It contains many elements wholly unknown elsewhere on the continent. 
It furnishes full data with which to close the already prolix debate on the 
exact a’ge and stratigraphic position of the uppermost Paleozoic beds of Kansas 
and other parts of the country. It is particularly important at this time as 
connecting the succession of the Mississippi province with that of the Far 
West. By contrast it emphasizes the insignificance of our eastern Carbonic 
representatives. 
It was recently shown* that while few estimates on the maximum measure- 
ment of the Carbonic rocks of the Southwest ventured above 2,000 feet there 
really existed of these sediments in New Mexico the enormous thickness of 
more than 6,000 feet. 
Although there have been many notes published on the Carbonic rocks of 
the Southwest there has never been any serious attempt to correlate the 
results of the various disconnected observations. Only lately have investiga- 
tions of broad character made reasonably exact geologic correlation in the region 
possible. While it is, perhaps, as yet premature to venture beyond the pro- 
vincial series in the detailed consideration of the Carbonic formations of the 
Rio Grande region, there are certain terranal names which have long been 
locally applied that may be used. Some of them were not, possibly, so exactly 
defined as they should have been originally; but this fact could hardly be a 
valid excuse for the proposal of new names on no better grounds than the old 
ones and the use of some of these old names in entirely different senses. From 
such course only confusion can come. 
In its latest and most complete form the standard Carbonic section of the 
Rio Grande region, or of New Mexico, may be indicated as follows: 
*Journal of Geology, Vol. XIV, p. 147, 1906. 
