Art. ’V.] Herrick, Geology of New Mexico, 95 
time, and at least three well-defined epochs are at present rec- 
ognizable which may serve as guides to future observations, viz; 
1. The Austin-Del Rio system, or Schumard knobs ; an- 
cient volcanic necks or laccolites bordering the Rio Grande em- 
bayment, begun in later Cretaceous time, the lava sheets of 
which have been obliterated by erosion. 
2. The lava flows of the Raton system, which are fissure 
eruptions of Tertiary time, and which are only partly removed 
by erosion. 
3. The cinder cones and lava flows of the Capulin system, 
which are late pleistocene and which still maintain their original 
slope and extent.” 
The geological structure of the plateau is not a little per- 
plexing. The upper part of all the exposures seen for a thick- 
ness of over 50 feet is composed of a finely stratified sandstone 
and pebble series. In places this is indurated or cemented to 
form a crag, while in others it is quite loose and friable. The 
color at a distance is grey in evident contrast to the brown or 
red of the lower 50 to 75 feet exposed. The latter is a mass 
of finely stratified clay and fine sand without the pebbly layers. 
At the summit of the exposure is a band of marl varying from 
10 to 25 feet thick with beds of charcoal carrying plant remains. 
This seems in every respect to be similar to the marl previously 
described as forming the upper layer in the river valley, though 
there is a difference of over 400 feet in altitude. It might be 
supposed that the lower marl was derived from the older or that 
both had a common origin. This marl is well seen on the west- 
ern exposure of the mesa facing the Rio Puerco where it ex- 
tends to a point far to the north of the position of the craters 
of the eastern slope. It is also seen on the face presented to 
the Rio Grande a short distance below the craters and data 
are wanting to determine whether it underlies the flow. It is 
not found underlying the flows from the craters in the same rel- 
ative position to the mesa northwest of Bernalillo, nor does it 
appear under the lava sheets which form the wall of the canon 
next north of this mesa near the town of Santa Ana. The ex- 
posures last mentioned apparently are of the same age as those 
