746  PRE-CAMBRTAN    GEOLOGY    OF    NORTH   AMERICA. 
held  to  rest  unconformably  upon  the  Burnetian,  because  no  other 
terrane  within  the  Burnetian  has  structural  planes  or  breaks  follow- 
ing a  course  N.  75 c  W.,  while  every  other  axis  of  uplift  is  traceable 
through  the  rocks  of  the  Burnetian  system,  and  because  the  basal 
members  of  the  Fernandian  system  are  made  up  in  part  of  material 
apparently  derived  from  the  Burnetian  rocks.  That  the  Texian 
(Algonkian?)  system  rests  unconformably  upon  the  Fernandian  is 
concluded  from  facts  of  the  same  character  as  those  which  show  the 
discordance  between  the  Burnetian  and  the  Fernandian.  The  nearly 
due  north-south  strikes  of  these  rocks  are  commonly  peculiar  to  them, 
the  earlier  fractures  and  lines  of  uplift  being  invariably  absent,  but 
the  later  ones  can  be  more  or  less  distinctly  traced  through  the  mem- 
bers  of  this  system.  There  are  localities  exhibiting  the  juxtaposition 
of  the  Texian  with  the  underlying  Fernandian,  in  which  the  non- 
conformity between  the  two  is  seen.  These  relations  are  seen  south 
and  southeast  of  Packsaddle  Mountain,  southwest  of  Sharp  Moun- 
tain, in  portions  of  the  country  north  of  Lockhart  Mountain,  north 
and  northeast  of  Mason,  in  the  Beaver  Creek  valley,  and  elsewhere 
in  Mason  County.  Further,  the  derivative  character  of  the  Texian 
beds  is  a  marked  feature.  In  the  Fernandian  is  a  great  development 
of  magnetites.  While  these  deposits  appear  to  be  in  discontinuous 
lenses  or  bosses  across  the  region,  there  is  almost  always  an  indication 
of  continuity  in  the  shape  of  a  line  of  ferruginous  soil  or  other  land- 
mark. The  iron  deposits  have  above  them  carbonaceous  and  calca- 
reous beds  and  below  them  quartzose  beds. 
Osann,87  in  1896,  gives  the  geology  and  petrography  of  the  Apache 
(Davis)  Mountains  of  western  Texas.  The  oldest  rocks  found  therein 
are  the  crystalline  schists,  which  compose  the  greater  part  of  the 
Carrizo  and  Van  Horn  mountains.  Here  is  found  a  great  set  of 
coarsely  crystalline  gneiss,  mica  schist,  and  associated  schistose  rocks. 
These  have  in  general  a  parallel  northwest-southeast  strike,  which 
agrees  with  the  axis  of  the  range.  Following  Professor  von  Streeru- 
witz,  Osann  places  these  with  the  fundamental  rocks. 
Walcott,88  in  1899,  states  that  the  Llano  series  of  Texas  is  a  series 
of  alternating  sandy  shales,  sandstone,  and  limestone,  very  similar  to 
those  of  the  Grand  Canyon  pre-Cambrian  series  and  overlain  by  a 
middle  Cambrian  sandstone  similar  to  the  Tonto  sandstone  of  the 
Grand  Canyon  district.  No  fossils  have  been  found  in  these  rocks, 
but  no  systematic  search  has  been  made. 
Richardson,89  in  190-t,  describes  the  pre-Cambrian  (?)  rocks  in 
El  Paso  County,  Tex.,  and  he  has  prepared  the  following  summary 
for  this  bulletin: 
There  are  two  areas  in  which  rocks  of  probable  pre-Cambrian  age 
are  exposed,  one  in  the  Franklin  Mountains  and  the  other  south  of 
