340 The American Geologist. June, 1900 
of these two members. The red bed escarpments extend far 
westward and turning south, from the western boundary of 
a considerable low plain south of the railroad and west of 
Mesa Lucero. This plain is covered for a large part by ba- 
saltic flows whose origin is in a series of lava cones and up- 
lifts extending far to the south. Permian strata rise from 
the plain here and there and at its southern end is a consider- 
able stretch of white (gypsiferous?) marl, reminding one of the 
region of the "white sands" in Otero county. In the low hills 
south of this plain the lime and sandstone of the Permian ap- 
pear and are greatly altered by the basaltic instrusives. Mesa 
Lucero apparently is formed from rocks of the red series cap- 
ped by Cretaceous, and the sam.e may be said of the great 
ridge or monocline which continues south for over twenty 
miles. The greater part of this range is lava-covered at the 
north and in its eastern exposure is exhibited the gypsiferous 
and saline series in a most interesting manner, though much 
broken by faults. East of a valley from five to eight miles 
wide the Carboniferous limestone forms a second prominent 
range v/hich is cut at frequent intervals by cross valleys. Here 
one may collect the usual assemblage of Carboniferous and 
Permo-carboniferous fossils as well as in the ranges to the east 
of the river. Salt water is found in many springs lying be- 
tween these ridges. The thirsty traveler is apprised of this 
unwelcomed fact even at a distance by the absence of the 
tracks about the pools and streams of clear water. The red 
bed series here will well reward study, both from a geological 
and from an economic standpoint. 
West of the great monocline is a high fertile valley in the 
rocks of the red series, which are everywhere covered by basalt. 
The decomposing basalt affords the material for the soil that 
supports excellent "grama grass." Still westward extends the 
great lava area, in unbroken blackness, covering hundreds of 
square miles. Our route took us down the valley east of the 
great monocline as far as to the Rio Salado. It was interest- 
ing to note the great dykes of porphyritic instrusive that strike 
north for many miles, at the eastern foot of this ridge. The 
main dyke is in some places 20 to 30 feet wide and rises above 
the soft sandstone and shale of the Cretaceous, which is at 
the surface in the southern part of the valley, in mural and 
