66 GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
GENERAL OBSERVATIONS ON THE CARBONIFEROUS FORMATION. 
The Carboniferous may be regarded as the geological horizon for the line, as indeed it is for 
the whole wide region west of the Mississippi river and the Anahuachian chain. It lies at the 
basis of all the non-metamorphic sedimentary strata, and is found at convenient points for geo- 
logical reference along the entire line. 
Disturbances to which the formation has been subjected.—If we cast our eyes upon the geologi- 
cal map and section, it is at once apparent that the principal orographic features of the conti- 
nent have been produced since the Carboniferous era. There is also a region which appears to 
have remained in a state of comparative quiescence since it was submerged by a carboniferous 
sea. "This region is that of the Aztec mountains, and eastwardly from them, towards the vol- 
cano of San Francisco. ‘The lines of the principal disturbance and uplift are those of the central 
chains—the Sierra Madre and the Santa Fé and Albuquerque mountains. Along these lines 
the carboniferous limestone and associate sandstones or shales are upraised at angles of thirty to 
forty degrees, and dip away from the central line of granitic rock. At the Albuquerque mount- 
ains the mountain limestone was even found at the height of 12,000 feet, forming the summit _ 
of the range. The general direction of these lines of uplift of the strata is nearly north and 
south, conforming to the direction of the ranges. The Sierra Madre, however, diverges towards 
the west, and its direction may be regarded as north 20° west. 
Another line of disturbance is found in the chain of slight elevations commencing at the 
Witchita mountains and extending in a direction a few degrees north of east to the Arkansas 
river. Along this line the strata are not raised to a very great height, but the trends of all the 
ridges and valleys in the carboniferous limestone and sandstone appear to be nearly coincident 
DARDANELLE ROCK. 
with it. Delaware mountain, which is one of this system, is uplifted, and the direction, ac- 
cording to Mr. Marcou, is N.N.E. and S.S. W. This is a greater deflection to the north than 
is indicated by the topography of the vicinity. It is possible that there is a line of uplift in a 
northeast and southwest direction, and that the main granitic axis, extending from the Washita - 
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