COAL  BETWEEN  DURANGO,   COLO.,  AND   MONERO,.  N.   MEX.       353 
manufacture  of  good  coke.  However,  the  Mesaverde  is  barren  of 
workable  coal  in  the  northeastern  part  of  T.  35  N.;  R.  8  W.,  and  is 
not  known  to  contain  a  single  workable  bed  around  the  northeast  side 
of  the  basin  for  a  distance  of  more  than  60  miles  along  the  outcrop. 
In  this  distance  the  formation  shows  remarkable  thinning,  and  along 
Piedra  River  it  is  less  than  400  feet  thick.  The  next  occurrence  of 
workable  Mesaverde  coal  beds  is  in  the  vicinity  of  Monero,  N.  Mex.; 
and  to  the  south  on  the  Apache  Indian  reservation  and  the  Tierra 
Amarilla  grant. 
The  Laramie  formation,  on  the  other  hand,  contains  coals  of  lesser 
value  than  the  Mesaverde  in  the  Durango  district,  and  shows  workable 
beds  along  its  entire  line  of  outcrop  from  Durango  to  the  Apache 
reservation.  The  Laramie  coal  is  of  medium  grade  over  most  of  the 
area,  and  is  classed  as  subbituminous  (" black  lignite"),  though  an 
analysis  of  Laramie  coal  along  upper  Beaver  Creek,  in  T.  35  N., 
R.  6  W.,  closely  approaches  that  of  a  bituminous  coal. 
The  outcrops  of  the  Mesaverde  and  Laramie  formations  are  repre- 
sented by  hogbacks  and  bold  escarpments,  with  intervening  valleys 
of  Lewis  shale.  The  two  escarpments  are  roughly  parallel  and 
extend  eastward  to  the  southern  part  of  T.  35  N.,  R.  5  W.  From  this 
vicinity  eastward  the  boundaries  separate,  being  at  some  points  as 
much  as  8  miles  apart. 
The  Dakota  at  most  places  forms  a  broad  dip  slope,  from  which  the 
Mancos  shale  has  been  entirely  eroded,  along  with  the  Mesaverde 
toward  the  interior  of  the  basin. 
Overlying  the  Laramie  are  the  Tertiary  rocks,  having  a  thickness 
of  about  2,500  feet  and  at  places  forming  a  line  of  high  hills  near  the 
Laramie  escarpment.  In  the  vicinity  of  Durango  a  series  of  con- 
glomerate beds  about  300  feet  thick  at  the  base  of  the  Tertiary  were 
named  by  Cross  a  the  Animas  formation.  These  are  well  exposed  on 
Animas  River  at  Carbon  Junction,  below  Durango,  but  they  were 
not  recognized  east  of  Piedra  River  and  apparently  are  locally  devel- 
oped in  the  vicinity  of  the  type  locality.  Toward  the  interior  of  the 
basin  the  Tertiary  forms  high  broken  hills  of  smooth  outline,  covered 
largely  by  pine  and  pifion  trees. 
STRUCTURE. 
The  dips  of  the  rocks  around  this  side  of  the  San  Juan  Basin  differ 
considerably  in  different  areas,  in  both  direction  and  degree.  The 
general  direction,  however,  is  south  and  west  of  south,  away  from  the 
San  Juan  Mountains  and  toward  the  interior  of  the  basin.  From 
T.  35  N.,  R.  8  W.,  to  T.  35  N.,  R.  5  W.,  the  dips  increase  from  30° 
to  50°.  Farther  east  the  dips  decrease  slightly,  and  gradually  change 
to  west  of  south  on  the  east  side  of  the  basin. 
<« Cross,  Whitman,  La  PJata  folio  (No.  CO),  Geologic  Atlas  U.  S.,  U.  S.  Geol.  Survey,  1899. 
71497— Hull.  341—09 23 
