Jemes — Albuquerque, N. Mex. — Reagan. 103 
teen miles to the southwest of the Jemez hot springs; and the 
San Isidro springs farther south are mostly cold. What caus- 
es the temperature to decrease on either side of Pelado as the 
distance from that mountain increases? The solution seems 
to be this : As has already been stated, Pelado was once the 
centre of a volcanic area, as the remains of the tufa flows and 
crater walls attest. Long since these craters ceased to be act- 
ive; but their reservoirs are still hot. The percolating waters 
then on coming in contact with the heated rocks come to the 
surface as hot or warm springs, thus perpetuating volcanic 
activity in the secondary stage. The farther the springs are 
from this volcanic area the cooler they become till at San Ysi- 
dro they are cold. 
The Tufa Flows. — A tufa flow covers the Jemez plateau 
as far as visited. It also extends south over the Red Beds as 
far as Canyon de los Jemez. The tufa deposit on the Red Bed 
triangle between Canyons Guadalupe and San Diego is from 
one hundred to two hundred feet in thickness. It was hurled 
out of the volcanoes at the foot of Pelado and in the Valle 
Grande country. Some of these volcanoes, as we have seen, 
are of great size and the leveling and falling of their craters 
has made the Great Valley (Valle Grande) country. 
Age of the Tufa of the Jemez Mountains. — In speaking of 
the age of the tufas of this region. Prof. William Jenks in the 
New Mexico Mining Record says : 
"In the Jemez range of mountains of which the Cochiti 
range is relatively a part, the pumiceous tuff was erupted dur- 
ing or at the close of the Jura-trias (Red Bed) period. We 
find there in a clear order, a base or central axis of red granite 
(red feldspathic porphyry) Carboniferous limestone, Permian 
and Jura-trias red and white sandstones and variegated shales, 
with superincumbent pumiceous tuff." 
Prof. Jenks in the Sunbeam, of Bland, New Mexico, Nov. 
1st, 1899, writes again concerning the age of these tufa flows 
and says : 
"I cannot imagine that this tufa flow so far as the Jemez 
and Cochiti mountains are concerned was later than prc-Creta- 
ceous ; for, as the liigher portions of these mountains had been 
occupied by the Cretaceous formations, some small remnant 
of it would be found somewhere within the area. For mvself, 
