Jcniez — Albuquerque^ N. Me.v. — Regan. 8i 
The Pucrco Marls. — In examining the Jemez-Albuquerque 
geological region described in these pages, several patches of 
grey, greenish and pinkish marls were noticed. One patch is 
east and southeast of Mesa Blanco ; a second is in the valley of 
Salt river, north of Mesa Blanco and south of the spring Ojo 
del Espiritu Santo ; a third area lies between the top of the 
divide west of Salt river and Cabizon ; and a fourth, as we 
have seen, is the country rock from the head waters of Salt 
river north to the head waters of the Rio Puerco. These pink- 
ish deposits were the puzzle of the whole geological research. 
Their stratigraphic position was readily determined to be at 
the top of the Fort Union ; but where the Fort Union is want- 
ing they repose directly upon the Fox Hills ; and in either of 
the above cases, they seem to be conformable with the form- 
ation they overlie except in the first case mentioned — the area 
to the east of Mesa Blanco. This formation, in part at least, 
there overlies the Jurassic. 
To give these marls a position geologically is a difficult 
task. In places as has been stated, they lie apparently con- 
formable on the Fox Hills, at other places on the Fort Union, 
and at still others unconformable on the Jurassic. Their being 
practically nonfossiliferous also makes the task the more diffi- 
cult. On their geological position geologists differ widely. 
In speaking of the geological position that the Puerco 
marls occupy Dr. Smith says : 
"The Puerco formation is located in northwestern New 
Mexico at the head waters of the Rio Puerco. . . . The rocks 
of this formation consist of sandstone and grey and green 
marls. The formation is thus characterized by Wortman : 
'The thickness of the beds is roughly estimated at 800 to 1000 
feet ; and as far as can be observed, they lie conformably on 
the Laramie.' "" 
Concerning the same formation and its geological position 
Endlich says : 
"It is entirely conformable with the Fox Hills, . . . From 
the evidence obtained by professor Cope farther south [at 
Nacimiento on the Rio Puerco] and the negative evidence in 
our own district, there is scarcely any doubt but that the posi- 
tion assigned to their group at the base of the Tertiary is a cor- 
