104 The American Geologist. February, laos. 
I have never seen the shghtest trace of anything later than 
Jura-Trias." (Red Bed series) ; "and tufa covers these 
beds, but never covers, so far as I know, the Cretaceous or 
Tertiary formations on the edge of the ranges."* 
Dr. C. L. Herrick, then president of the University of New 
Mexico, took issue with Prof. Jenks, beHeving that the tufa 
was of Cretaceous age ; and asked the writer by letter to in- 
vestigate the age of the tufa, which he did with the following 
results : 
Tufa was found covering both the Carboniferous rocks and 
Red Beds, and also the granite plateau and the metamorphic 
rocks on the mountain flanks where the Carboniferous and Red 
Beds are wanting; but no tufa, in situ, was found on rocks 
of an age younger than that of the Red Beds. The investiga- 
tion favors Prof. Jenks' opinion. The tufa therefore, seems to 
be at least pre-Cretaceous.f 
The Basaltic Volcanoes. — The basaltic volcanoes and their 
lava flows are arranged in two series, the Rio Puerco, and 
the Rio Grande. They will receive consideration in the order 
given. 
The Rio Puerco Series. — The Rio Puerco series of basaltic 
volcanoes begins at Cabizon with Mt. Cabizon as the north- 
east crater and continues on in a southwestern direction. The 
plugs of the craters now dot the country, Mt. Cabizon being 
the largest one, thus indicating, in a way, the amount of ero- 
sion that has taken place since these craters ceased to be active. 
The lava, for the most part, has been almost wholly removed. 
A careful examination reveals the fact that the volcanic rocks 
protrude through Cretaceous strata, and moreover that no lava 
of these eruptions are in situ on Tertiary deposits, though 
CO marls. The conclusion drawn from the observations is that 
they rest in places on the Fort Union and possibly on the Puer- 
these volcanoes are post-Cretaceous in age. 
The Rio Grande Series of Basaltic Volcanoes. — The Rio 
Grande series of basaltic volcanoes has a general northerly 
and southerly course. Their direction is the result of a seismic 
disturbance, opening up a fissure that can be traced from a 
* Prof. Jenks has prospected the entire Jemez range, and is to-day one of 
the leading stockholders in the Cochiti Gold Mining Company at Bland, New 
Mexico. 
t There are several tufa patches near Albuquerque, all of which seem to be 
post-tertiary in age. 
