martin.]  PETEOLEUM    FIELDS    OF    ALASKA.  377 
but  the  remainder  of   the  series   is  conformable  throughout  and  is 
gently  and  simply  folded.     The  general  section  is  as  follows: 
General  section  of  Chigmit  Mountains. 
Feet. 
1.  Sandstone,  shale,  and  conglomerate  with  fossil  trees 100  ? 
2.  Volcanic  rocks  (andesite,  etc.)  with  some  interbedded  shale 2,  000  ? 
3.  Shale 580 
4.  Volcanic  rocks  (andesite  or  agglomerate) 300 
5.  Shale 1,  6504- 
6.  Coarse  crystalline  rocks. 
The  crystalline  rocks  of  the  Chigmit  Mountains  extend  along  the 
entire  western  shore  of  Enochkin  Bay,  and  both  shores  of  the  northern 
arm  of  that  bay.  There  is  considerable  variety  to  the  series,  but  gran- 
ite and  rocks  similar  in  texture  and  general  appearance  predominate. 
Jurassic  shales. — The  rocks  overlying-  the  crystallines  consist  of  a 
thin  conglomerate  at  the  base,  followed  by  more  than  1,600  feet  of  dark 
sandy  shales  with  occasional  bands  of  sandstone,  conglomerate,  and 
limestone  and  many  fossil  beds;  they  are  well  exposed  in  the  cliff's  on 
the  east  shore  of  Enochkin  Bay.  Rocks  of  the  same  lithologic  char- 
acter extend  along  the  strike  northeastward  from  these  exposures, 
passing  the  heads  of  Oil  and  Dry  bays  to  Chinitua  Bay.  They  have 
not  been  followed  beyond  the  north  shore  of  Chinitua  Bay  by  the 
writer,  but  from  the  great  thickness  exposed  it  is  evident  that  the}^ 
must  extend  a  considerable  distance.  Rocks  of  similar  lithologic  char- 
acter have  also  been  reported  from  the  vicinity  of  Snug  Harbor. 
Fossils  are  distributed  throughout  the  formation  and  show  the  age  to 
be  middle  Jurassic. 
Volcanic  flows  and  agglomerate. — The  Jurassic  shales  are  overlain 
by  a  series  of  volcanic  flows,  probably  of  andesite,  and  by  coarse 
agglomerate.  There  is  some  interbedded  shale.  The  agglomerate 
seems  to  be  confined  to  the  shore  of  Enochkin  Bay.  These  rocks  form 
the  high  coastal  ridge  which  extends  from  Enochkin  Bay  to  and 
beyond  Chinitua  Bay,  their  total  thickness  being  probably  more  than 
2,000  feet. 
Structure. — The  structure  of  this  region  consists  of  a  broad,  low, 
somewhat  undulated  anticline  parallel  to  the  shore  of  Cook  Inlet  and 
to  the  general  line  of  the  eastern  front  of  the  Chigmit  Mountains, 
followed  on  the  west  by  a  narrow  syncline,  be}^ond  which  is  a  second, 
very  closely  folded  and  probably  faulted  anticline.  The  dip  in  the 
broad,  easternmost  anticline  is  moderate  in  amount  and  very  regular, 
except  on  the  crest  of  the  fold,  where  it  is  undulating,  but  is  not  in 
excess  of  10°.  On  the  eastern  limb  the  dip  varies  from  20°  to  28°, 
diminishing  as  the  shore  is  approached,  and  on  some  of  the  long  points 
and  islands  becoming  almost  or  quite  horizontal.  The  steepest  dip  in 
the  southwestern  part  of   the  field  was  observed  on   the   shore   of 
