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IOWA ACADEMY OF SCIENCE 
GENERAL RIO GRANDE SECTION OF CARBONIC TERRANES. 
Time Divisions 
Provincial Series 
Formations 
Rocks 
DATE 
Cimarronian 
Moencopie 
Shales 
Sandstones 
Pecos 
Shales 
Guadalupan 
CnpifaTi 
Limestones 
Eddy 
Sandstones 
MID 
Maderan 
Bernalillo 
Shales 
Hueco (upper).— 
Oscuro 
Limestones 
Limestones 
Manzanan 
MO'Sca — —J— 
Coyote 
Montosn 
Limestones 
Sandstones 
Limestones 
Sfludia 
Shales 
Ladronesian 
Alamito 
Shales 
EARLY 
Socorran 
Sierra 
Lake Valley 
Grande 
Limestones 
Limestones 
Limestones 
The presence of marked planes of unconformity between all of the several 
serial divisions is especially significant. It points to still other unknown and 
important representatives to make the American section complete. How great 
are the terranal representatives of these intervals can at present only be sur- 
mised. In northern New Mexico the unconformity plane between the Maderan 
and Cimarronian series is known, 200 miles to the southward, to be represented 
by over 3,000 feet of sediments. The remnants of the true coal-bearing series, 
corresponding to the lower productive coal measures of the Mississippi valley 
is believed to have been once of great thickness and extent. Under similar 
conditions an erosion interval north of the Ozark dome at the base of the Des 
Moines series is known to be represented farther south in central Arkansas 
by sediments the thickness of which is more than 10,000 feet.* * In the South- 
west the depositional equivalents of the Carbonic unconformities may equal or 
even greatly exceed in thickness that of the present known section. 
The Socorran series corresponds in a general way to the lower part of the 
original Mississippian series of Missouri and Illinois. The Ladronesian, Man- 
zanan, and Maderan series might be included in the world-wide Pennsylvanian 
division of the United States Geological Survey. The Guadalupan and Cimar- 
ronian series have no representation in the East; and the latter in the Missis- 
sippi valley only in western Kansas. 
Three important subdivisions of the Socorran series have thus far been 
recognized.! These find their best development in the vicinity of Lake Valley, 
in southwestern New Mexico. There are good reasons for believing that other 
formations of this series exist nearby. These formations are the Grande, Lake 
*The heavy lines indicate planes of unconformity. The Eddy sandstones may more 
properly belong to the Maderan possibly co-extensive with the Bernalillo shales and 
sandstones ; there are reasons for believing that marked line of unconformity exists at 
the base of the Capitan limestone. All of the unconformities represent erosion epochs, 
except that between the Maderan and Manzanan which is apparently an overlap. There 
are several planes of unconformity in the Maderan section. 
*Bull. Geol. Soc. America, Vol. XII, pp. 173-196, 1901. 
tTrans. American Insti. Min. Engin., Vol. XXXIX, 1908. 
