340         CONTRIBUTIONS   TO   ECONOMIC   GEOLOGY,   1907,   PART   II. 
mapping.  The  upper  escarpment  could  not  be  traced  with  certainty. 
The  prominent  escarpment  of  the  Wasatch  to  the  north  follows  in  a 
general  way  parallel  to  these  escarpments.  Near  a  small  pond,  about 
7  miles  N.  76°  E.  of  Ensino  Spring,  vertebrate  fossils  were  collected 
from  25  feet  of  dark  and  gray  argillaceous  sand  and  shale  immediately 
overlying  the  basal  escarpment  sandstone.  A  careful  study  of  these 
fossils  has  been  made  by  J.  W.  Gidley,  of  the  United  States  National 
Museum,  and  the  specimens  have  been  compared  with  original 
material  in  the  American  Museum  of  Natural  History,  New  York. 
This  comparison  definitely  places  them  in  the  Torrejon  formation.0 
The  Laramie  reappears  from  beneath  the  lower  escarpment,  striking 
almost  at  right  angles  with  it,  thus  bringing  out  a  marked  uncon- 
formity between  the  two.  It  does  not  follow  from  the  fossils  that  the 
lower  escarpment  is  of  Torrejon  age.  It  is  probable  that  there  is  an 
unconformity  between  the  Puerco  and  the  Torrejon.  This  accounts 
for  the  Torrejon  fossils  immediately  above  the  basal  escarpment  sand- 
stone, which  is  in  all  probability  the  lowest  member  of  the  Puerco.  It 
is  certainly  at  the  base  of  an  800-foot  mass  below  the  Wasatch, 
exposed  along  the  headwaters  of  Rio  Puerco,  as  originally  described 
by  Cope.6  Along  Rio  Puerco  the  base  of  the  Wasatch  is  750  feet 
above  the  top  of  the  basal  Puerco  sandstone.  At  the  point  where  the 
Torrejon  fossils  were  collected  the  base  of  the  Wasatch,  as  determined 
by  both  stratigraphic  relationship  and  fossil  evidence,  is  only  135  feet 
above  the  top  of  the  same  sandstone.  Hence  the  800  feet  of  the 
original  Puerco  is  represented  by  only  the  basal  sandstone,  from  30 
to  50  feet  thick,  unconformably  overlying  the  Laramie.  This  sand- 
stone is  unconformably  overlain  by  110  feet  of  Torrejon,  above  which, 
also  unconformably,  lies  the  Wasatch.  Space  does  not  permit  a 
detailed  discussion  of  the  Tertiary  rocks  in  this  preliminary  report, 
but  such  a  discussion  will  appear  as  a  chapter  in  the  report  on  the 
entire  field,  to  be  published  as  a  separate  bulletin  of  the  Survey. 
QUATERNARY    DEPOSITS. 
The  local  terrace  deposits,  granite  wash,  etc.,  occurring  between 
Gallina  and  Cuba  and  resting  in  places  upon  the  Wasatch  beds,  also  the 
alluvium  and  adobe  clays  along  the  present  drainage  ways,  used  as 
building  materials  by  the  natives,  are  classed  as  Quaternary. 
STRUCTURE. 
Mention  has  been  made  of  the  hogbacks  composed  of  steeply 
dipping  strata  along  the  crystalline  rocks  of  the  Sierra  Nacimiento. 
The  Cretaceous  rocks  in  the  vicinity  of  Gallina  dip  to  the  west  at  an 
angle  of  60°;  farther  south  the  dips  are  steeper,  reaching  90°  near 
a  Torrejon  is  a  name  proposed  by  J.  L.  Wortman  (Bull.  Am.  Mus.  Nat.  Hist.,  vol.  9, 1897,  pp.  260-261) 
for  a  fossil  zone  at  the  top  of  the  original  Puerco  of  Cope. 
bCope,  E.  D.,  Kept.  Chief  Eng.,  1875,  pt.  2,  p.  1008. 
