366         CONTRIBUTIONS   TO   ECONOMIC   GEOLOGY,   1907,   PART  II. 
coal  beds  between  Gallup  and  San  Mateo,  the  Mancos  and  the  Mesa- 
verde.  All  the  fossils  so  far  collected  by  previous  parties  and  by  the 
writer  during  the  last  season  confirm  Shaler's  determination  that  the 
coal  beds  of  the  Mancos  are  limited  to  the  lower  part,  and  conse- 
quently are  of  Colorado  age. 
Only  the  lower  part  of  the  Mesaverde  formation  is  present  in  the 
escarpment  between  Gallup  and  San  Mateo.  The  upper  portion  is 
eroded  for  a  distance  of  40  miles  to  the  north,  and  forms  an  escarp- 
ment along  Rio  Chaco  roughly  parallel  with  the  margin  of  the  field 
and  in  close  proximity  to  the  outcrops  of  the  Lewis  and  Laramie 
formations. 
The  following  table  includes  the  formations  of  the  Cretaceous  system 
exposed  between  Gallup  and  San  Mateo : 
Generalized  section  of  a  portion  of  the  Cretaceous  rocks  between  Gallup  and  San  Mateo, 
N.  Mex. 
Mesaverde  formation,  lower  part  (1,000  feet):  Massive  sandstone,  alternating  with 
thin  clay  and  argillaceous  shales  and  bearing  workable  coal  beds. 
Mancos  shale  (800  feet) : 
Massive  sandstone,  arenaceous  shale,  and  coal  beds,  workable  in  central  part  of 
the  area  (500  feet). 
Drab  clay  shale  and  thin  sandstones  (300  feet). 
Dakota  sandstone  (200  feet):  Light-gray,  hard  sandstone  at  top  and  bottom.     Alter- 
nating thin  beds  of  sandstone  and  shale,  with  some  bituminous  shale  and  a  few 
irregular  coal  beds  of  no  commercial  importance. 
It  is  probable  that  the  upper  part  of  the  Mesaverde,  corresponding 
to  the  formation  along  Rio  Chaco,  is  present  in  the  Gallup  district 
and  farther  southward  in  the  Zufii  Basin.  Further  work  will  doubt- 
less be  necessary  before  the  exact  correlation  of  these  rocks  can 
be  made. 
Regarding  the  Dakota  coal,  it  seems  well  to  quote  the  following 
paragraph  of  Shaler's  report  relative  to  the  Gallup  district:" 
The  coals  of  the  Gallup  district  represent  three  formations — the  Dakota,  Mancos, 
and  Mesaverde.  Those  of  the  Mesaverde  are  the  most  valuable  and  the  only  ones 
at  present  mined.  The  Dakota  coal  was  examined  east  of  Gallup  in  the  southward- 
facing  escarpment  north  of  the  railroad,  but  was  found  to  be  thin  and  full  of  partings 
and  consequently  not  of  present  commercial  value. 
This  character  appears  to  hold  for  the  Dakota  throughout  the 
Gallup-San  Mateo  field. 
THE   COAL. 
There  has  been  no  development  of  the  coal  beds  in  most  of  the 
field  under  present  discussion,  mining  being  confined  entirely  to 
the  vicinity  of  Gallup.  For  a  description  of  the  mines  and  sections 
at  Gallup,  the  reader  is  referred  to  the  Schrader  and  Shaler  reports, 
a  Op.  Cit.,  p.  410. 
