Geology of Albuquerque, N. M. — Herrick. 41 
Fig. o. More distant view of the aeck of tlie BerualiUo volcano aud the 
lava-topped mesas beyond. 
poses on the red and grey Cretaceous strata, which remain 
nearly horizontal. The sources of these flows is not difficult 
to locate in local craters which penetrate the Cretaceous at 
various places. The erosion of the river has done a very use- 
ful service to the geologist, in removing, to a large extent, 
the soft strata about one of the old cones and exposing the 
true inwardness of the eruption when occurring in soft ma- 
terials. In fact, it may be said to afford the necessary supple- 
ment to the data from the Isleta volcano. Here, as in that 
case, the lava forced its way through the soft Cretaceous 
strata, and here also the outbreak seems to have been attended 
with a great flood of hot water which has redistributed the 
materials. In one place (PI. VI., Fig. i) erosion has exposed 
the "neck" or original column of lava which cooled in the 
throat of the crater, and one may see the long dykes of basalt 
radiating in various directions into the soft displaced sand 
(PI. VI., Fig. 2). These radiating dykes formed ribs to which 
the plastic sand mixed with fragments of the basalt adjusted 
itself. In the vicinity of these dykes there is often a small 
amount of metamorphism roughly proportionate to the 
thickness of the intruded mass. There is much reason to 
suppose that the other volcanoes of the valley arc not later 
than these mentioned. 
