IOWA ACADEMY OP SCIENCES. 
167 
The Sierra Oscura-San Andreas range presents some 
features which are quite different from those already men- 
tioned, which may be partly due to faulting at the time the 
blocks were tilted. The two parts of the range overlap 
somewhat, and dip in opposite directions. The major 
fault plane along which the block wa^ upraised lies on dif- 
ferent sides of the two parts of the range. Between the 
two parts is a flat plain, several miles wide, which, how- 
ever, is considerably elevated above the plains on either 
side of the great ridge. The mountains are capped by 
Carboniferous limestones; so also is the small plain 
between. The section appears to be as follows (figure 7): 
Fig. 7 . Fault Block between th« Sierra Oacura and San Andreas Range 
Displacement 2, 500 feet. 
GEOLOGICAL STRUCTURE OF THE JORNADA DEL 
MUERTO AND ADJOINING BOLSON PLAINS. 
BY CHARLES R. KEYES. 
The recent visits of a number of the members of the 
Academy to the Tulerosa district and contiguous plains in 
New Mexico makes it seem worth while to call attention 
to some of the major geologic structures of the region. 
The section represented below is in an east and west 
direction through the station of Engle on the Atchison, 
Topeka & Sante Ee railroad, reaching beyond Alamagorda 
on the El Paso & Northeastern railroad. 
