524 The American Naturalist. [June, 
A RECENT LAVA FLOW IN NEW MEXICO. 
BY RALPH S. TARR. 
1s the southern central part of New Mexico, on the mail road 
from Carthage to Fort Stanton, and about fifty miles east of 
the Rio Grande, there is a flow of basalt having every evidence 
of being very recent. It has a north and south extension of 
more than thirty miles, and a width varying from one-fourth of a 
mile to four miles. The point of extrusion is a small cone stand- 
ing at the northern end. The period of eruption was brief, and 
the material extravasated has barely succeeded in filling a narrow 
valley. Some time ago I crossed this region, and made a few 
observations, which, though by no means complete, are deemed 
worthy of presentation, with the hope that the notice may serve 
to call the attention of some one to the interesting phenomena, 
and thus lead to a more detailed study. 
The lava flow is situated in a basin of interior drainage, almost 
completely enclosed by mountains. This basin, which varies in 
width from ten to thirty miles, and has a north and south exten- 
sion of fully one hundred miles, is bounded by the Oscura and 
Jicarilla Mountains on the north, the White and Sacramento 
Mountains on the east, the Huego and El Paso Mountains on the 
south, and the Organs and San Andreas on the west. The exact 
area of interior drainage cannot be told at present, but it must 
exceed one thousand square miles. On the foothills of the 
mountains are quite. distinct beaches, which with other evidence 
tend to prove that this basin is the site of one of the Quaternary 
lakes, of which there were others in this vicinity. The loose 
gravels of the basin quickly absorb all the moisture which falls 
upon the surface, and the mountain torrents rarely escape far into 
the plain before being entirely absorbed, A few never-failing 
mountain brooks enter from the White Mountains on the northeast 
side, and they also sink into the soil within a few miles of their 
outlets from the mountain gorges. At the lowest part of the basin 
are some shallow salt lakes and marshes of the “playa” type, 
