Jeinc:: — Albuquerque, N. Mex. — Regan. 83 
But in all cases in which they overlie the Fort Union, they 
grade insensibly into it. This was the case throughout the 
entire area examined by the writer; and the whole was called 
Fort Union by him while in the field. They therefore seem to 
be upper Fort Union and represent a transition between the 
Fort Union and the Tertiary. The fossils found by Cope 
(see above) seem to bear out this conclusion. They seem 
to be the top of the Cretaceous rather than the base of the 
Tertiary. 
The Tertiary Strata. 
On leaving the mountain districts, except west of the Naci- 
miento mountains, the Tertiary is the prevailing country rock 
where it is not covered with lava or Pleistocene deposits. 
Throughout its entire area it is fissured and faulted ; the rivers 
of the country in their process of base leveling have chiseled 
their channels deep into it. The great dike and the Rio Grande 
series of volcanoes penetrate its surface ; and lava flows, cover- 
ing hundreds of square miles, are superimposed on it. The dip 
of the whole formation, where dip is noticeable, is away from 
the mountains at an angle of about 15°, except at Jemez Pueblo 
where in the valley the strata dip north. This Tertiary is a 
"bad land" country ; where the lava is superimposed on it it is 
of the "mal pais" type; and where the lava is wanting, espec- 
ially along the break lines, "mauvaisses terres." 
Having mentioned the Tertiary in a general way, we will 
proceed to consider it more in detail. Two epochs of the Ter- 
tiary are represented here, the Eocene and the Pliocene. 
The Eocene Formation. — The Eocene formation at one 
time covered the greater part of this region, but a faulting and 
folding of the strata in different parts left basins on a grand 
scale, which in Pliocene times were lakes. The Eocene coun- 
try rock now is the entire Zia mesa between the Rio Grande 
and the Rio Puerco north to the Jemez river and Mesa Blanco 
and west of a point below Cabizon. The Eocene also underlies 
the great lava sheet to the west of San Felipe and also the lava- 
sheet of the tongue-shaped mesa which projects south from the 
Cochiti range. The thickness of this formation was not as- 
certained, though 1000 feet of it in vertical section are exposed 
along the west break of the tongue-shaped mesa above mention- 
ed. The strata throughout are soft red and grav sandstones, 
