224 
IOWA ACADEMY OF SCIENCE 
Of the four parts into which the Tertiary time is subdivided the 
Oligocene has not been as yet recognized by sediments anywhere 
within the limits of New Mexico. The Eocene, or Early Tertiary, 
period is represented by at least four important formations and it 
is quite likely that further differentiation will be found advan- 
tageous. 
It is proposed to call the basal portion of the Early Tertiary 
section of New Mexico the Nacimientan series. The term is par- 
ticularly appropriate as it means, in the Spanish language, birth. 
The title is taken from the great land grant known as San Joaquin 
del Nacimiento which lies in Rio Arriba and Bernalillo counties. 
Nearly the entire section of the New Mexican Eocene deposits 
occurs within the limits of this grant. The formation also stretches 
away to the northwestward from the foot of the Nacimiento range 
of mountains ; and the village of Nacimiento is built upon the rocks 
of this series. 
The Nacimientan series has a maximum thickness of not less than 
1,000 feet, divisible into at least two well-defined terranes; (1) 
Puerco marls, about 500 feet in thickness; and (2) the Torre j on 
sandstones about 200 feet thick. This series is believed to repre- 
sent a period that is earlier in point of time than any other Eocene 
deposits. The uppermost member of the Torre j on formation may be- 
long to the earliest or Midwayan stage but it is thought to be some- 
what earlier. Its corresponding European stage is the Cernaysian. 
In a general way the Nacimientan series covers the better known 
subdivision of the Puerco beds of Cope, but it includes a consider- 
ably greater section. 
The Chaman series embraces two important formations and some 
of less vertical extent. It includes the major portion of the New 
Mexican section generally that has gone under the title of the 
Wasatch beds. 
To the lower part of the series Newberry early* gave the name of 
Canyon Largo beds. “Long Canyon” drains the interior of the great 
Eocene plateau of northwestern New Mexico. The canadas of its 
headwaters reach to the very crest of the high, eastward facing es- 
carpment overlooking the valley of the Rio Gallinas, in Sandoval 
county. From the top of the facade a vast mesa or inclined plain 
stretches away a hundred and fifty miles to the northwestward to 
beyond the Arizona line. This tilted plain is worn out on the beveled 
edges of Tertiary, Cretaceous, and Triassic strata which have a 
Macomb’s Exp. Green River, Geol. Rept., p. 1, 1876. 
