IRVING.] 
OURAY    DISTRICT,    COLORADO. 
67 
Below  this  come  the  variegated  shaly  series  of  the  McElnio  forma- 
tion. The  series  dips  into  the  hill  at  a  low  angle  of  from  5  to  10° 
slightly  to  the  east  of  north.  The  dip  is  much  steeper  locally.  The 
rocks  are  cut  by  a  number  of  dikes  of  dark-colored,  fine-grained 
porphyry,  probably  connected  with  the  monzonite  sill  above,  and  ore 
is  sometimes  found  beside  them,  although  more  frequently  widely 
separated. 
A  heavy  fault  fissure  filled  with  a  consolidated  breccia  similar  to 
that  observed  in  the  Bachelor  mine  runs  east  and  is  followed  by  the 
Quartz -monzonite 
porphyry 
500'  K' 
-I,  > 
Black  carbon 
aceous  shale 
40'± 
Fig.  4. — East-west  section  of  the  rocks  and  diagram  of  the  ore  bodies  in  the  American 
Nettie  mine,   Ouray,  Colo. 
main  tunnel  of  the  mine.  It  is  sometimes  simply  a  fault  fissure  with 
no  filling  material  in  it.  The  breccia  is  termed  a  "  dike,"  but  is  not 
correctly  so  considered.  It  is  the  impression  of  the  miners  that  the 
ore  emanates  from  this  fault  breccia  and  makes  out  from  it  into  the 
|  country  rock,  but  an  examination  of  the  mine  and  a  glance  at  the  mine 
map,  as  well  as  a  comparison  with  a  large  number  of  precisely  similar 
occurrences  in  quartzite,  where  no  fault  breccia  and  no  porphyry 
dikes  are  present,  shows  that  there  is  no  connection  between  the  two. 
