Lake Otero, N. M ex.— Merrick. i8i 
In describing- this basin one is forcibly reminded of Mr. 
I. C. Russell's account of lake Lahontan ; in Powell's Third An- 
nual Report; indeed, much of his description of the Great 
Basin applies, on a reduced scale, it is true, to the region in 
question. "No streams that rise within it carry their con- 
tribution to the ocean, but all the rain that falls inside the rim 
of the basin is returned again to the atmosphere, either by 
direct evaporation from the soil, or, after finding its way into 
some of the lakes that occupy the depressions of the irregular 
surface. The climate is dry and arid in the extreme." It has 
been a matter of frequent observation that during the early 
part of the rainy season clouds from which rain is falling in 
torrents will pass over such dry reaches of sand intensely 
heated by the sun and, on reaching their borders, the rain 
will fail to reach the earth and soon perhaps the cloud will 
cease to precipitate but may resume its occupation on reach- 
ing- the farther (cooler) side of the plain. 
The mountains bordering the lake basin conform to the 
"great basin type." "They are long narrow ridges usually 
bearing north and south, usually steep upon one side, where 
broken edges of the composing beds are exposed, but sloping 
on the other with a gentle angle conformable to the dip of the 
strata. They have been formed by the orographic tilting of 
blocks that are separated by profound faults, and they do not 
exhibit the synclinal structure commonly observed in moun- 
tains but are monoclinal instead." 
To this description it may be remarked that the structure 
in question is by no means limited to the Great Basin, for 
throughout a great part of New Mexico this is the type of 
mountain formed where Carboniferous and earlier strata are 
involved in the uplift. It is a mistake to suppose that this is 
essentially a monoclinic type. Anticlines exist on a grand 
scale but these arches grow coincidentally with vast erosion 
and faulting and were often greatly altered by later intrusion 
phenomena which, as I have repeatedly pointed out, com- 
monly chose one of the lateral axes of the anticline for the 
play of their disturbing forces. 
Much as it has been altered by late disturbances and 
enormous erosion and sedimentation, it is impossible to fail 
to recognize the anticline of the middle Rio Grande valley, for 
