742  PRE-CAMBE1A       GEOLOGY    OF    NORTH    AMERICA. 
western  end.  The  porphyry  and  aporhyolite  areas  occur  in  the  Ar- 
buckle  Mountains  proper,  in  the  western  end  of  the  uplift. 
In  the  Wichita  Mountains,  southern  Oklahoma,  pre-Cambrian  gran- 
ite, granite  porphyry,  and  gabbro  cut  by  diabase  form  a  considerable 
part  of  the  mountains.  Granite  is  the  principal  mountain-making 
rock  in  the  Wichita  region.  Its  area  is  greater  than  that  of  all  the 
other  igneous  rocks  combined,  and  is  about  equal  to  that  of  the  others 
and  the  older  Paleozoic  sediments.  It  makes  all  of  the  high  land  of 
the  Wichita,  Quana,  Devils  Canyon,  and  Headquarters  mountains, 
and  a  large  part  of  the  Raggedy  group. 
The  gabbro  is  exposed  for  the  most  part  in -the  valleys  or  on  the 
plains  which  surround  the  mountains.  The  granite  porphyry  com- 
prises practically  all  of  the  Carlton  Mountains,  the  igneous  mass 
lying  between  the  Cambro-Ordovician  limestone  hills  in  the  vicinity 
of  Blue  Canyon,  north  of  Mount  Scott,  and  some  hills  composed  of 
the  same  class  of  rocks  southwest  of  Fort  Sill. 
In  the  Wichita  Mountains,  as  in  the  Arbuckle  uplift,  the  middle 
Cambrian  sediments  lie  on  the  eroded  surface  of  the  igneous  rocks. 
The  basal  deposits  are  composed  to  a  large  extent  of  detrital  ma- 
terial from  the  contact  and  adjacent  igneous  rocks. 
SUMMARY    OF   PRESENT   KNOWLEDGE. 
Rocks  of  apparently  pre-Paleozoic  age  appear  at  two  localities: 
(1)  In  the  Arbuckle  Mountains  of  southern  Oklahoma,  where  granite, 
granite  porphyry,  and  aporhyolite  occur,  supposedly  of  pre-Cam- 
brian age.  The  granite,  called  the  Tishomingo  granite,  is  in  the  east- 
ern part  of  the  uplift,  while  the  granite  porphyry  is  in  the  western 
part.  Both  are  cut  by  basic  dikes.  (2)  In  the  Wichita  Mountains, 
southern  Oklahoma,  are  granite,  granite  porphyry,  and  gabbro,  cut 
by  diabase  dikes.  The  closest  correlation  yet  possible  is  a  tentative 
one  with  the  pre-Cambrian. 
SECTION   6.     TEXAS. 
SUMMARY    OF    LITERATURE. 
Roemer,76  in  1848,  mentions  granitic  rocks  at  several  points — 15 
miles  north  of  Fredericksburg,  on  the  banks  of  the  Llano,  in  the 
country  between  the  Llano  and  San  Saba,  and  between  Pedernales 
and  San  Saba  rivers.  These  granitic  rocks  are  surrounded  by  Paleo- 
zoic strata. 
Shumard,77  in  1860,  describes  rocks  in  Burnet  County  upon  which 
rest  directly  the  fossiliferous  Potsdam. 
Shumard,78  in  1861,  describes  the  Primordial  rocks  of  Texas  as* 
resting  upon  reddish  feldspathic  granite  very  similar  in  character 
and  composition  to  the  granites  of  Iron  Mountain,  Missouri. 
