376  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull.  225. 
COOK  INLET  PETROLEUM  FIELD. 
GEOGRAPHY. 
The  region  under  discussion  occupies  the  western  shore  of  Cook 
Inlet  from  the  foreland  on  the  north  side  of  the  entrance  of  Chinitua 
Bay  southwestward  for  about  40  miles  to  the  mouths  of  Enochkina 
and  [liamna  bays,  and  extends  inland,  with  a  maximum  width  of  about 
10  miles,  to  the  crystalline  rocks  at  the  eastern  front  of  the  Chigmit 
Mountains.  Its  coast  includes  the  deep  indentations  of  Chinitua, 
Enochkin,  and  Iliamna  bays  and  the  lesser  ones  of  Oil  and  Dry  bays. 
The  region  includes  a  high  mountain  range,  a  range  of  lower  hills, 
and  an  intervening  valley  region.  The  rugged  Chigmit  Mountains 
have  an  average  elevation  of  about  5,000  feet  and  are  parallel  to  the 
general  shore  of  the  inlet.  The  range  of  lower  hills,  unnamed,  extends 
from  the  mouth  of  Enochkin  Bay  northeastward  to  Snug  Harbor, 
paralleling  the  coast  at  the  distance  of  a  mile.  The  general  height  of 
these  hills  is  about  2,500  feet.  A  general  area  of  depression  occupies 
the  position  between  these  two  ranges.  This  consists  of  many  valleys 
drained  by  streams  flowing  into  the  bays  named  above,  and  of  irregular, 
low,  rounded  hills.  The  divides  between  the  drainage  systems  are  low 
and  permit  easy  portages.  The  streams  are  all  small,  for  the  most 
part  unnamed,  and  entirely  unnavigable. 
The  lowlands  are  covered  with  dense  vegetation  and  consist  of  about 
half  meadow  and  half  forest.  The  meadows  are  deeply  grassed  and 
are  dotted  with  groves  of  cottonwood  and  thickets  of  alder  and  willow. 
The  forests  consist  of  a  fair  growth  of  spruce  and  hemlock.  The 
tree  are  not  large,  but  are  straight  and  sound. 
A  wagon  road  has  been  built  from  the  lower  landing  point  of 
Enochkin  Bay  to  the  head  of  Oil  Bay,  and  there  are  cleared  trails  from 
the  head  of  Oil  Bay  to  Dry  Bay,  to  the  head  of  the  eastern  arm  of 
Enochkin  Bay,  and  to  a  point  on  the  shore  of  Enochkin  Bay  2  miles 
above  the  lower  landing.  There  are  also  two  trails  from  Dry  Bay  to 
the  shores  of  Chinitua  Bay,  and  a  portage  trail  from  the  head  of 
Enochkin  Bay  to  the  head  of  Chinitua  Bay. 
GEOLOGY. 
The  rocks  of  this  region  consist  of  a  zone  of  a  massive  c^stalline 
series  exposed  in  the  Chigmit  Mountains,  a  sedimentary  formation  of 
Jurassic  age  in  a  belt  east  of  them,  and  a  series  of  overlying  agglomer- 
ates, shales,  and  bedded  volcanic  flows,  which  are  exposed  in  the  coastal 
range  of  hills.  The  formations  lie  in  belts  parallel  to  the  coast.  The 
relation  of  the  sedimentaries  to  the  crystallines  is  complex  and  obscure, 
"  I  his  has  been  variously  spelled  as  Inerskin,  Innerskin,  Inischen,  and  Innisken,  but  as  here  given 
is  said  to  be  the  correct  spelling  of  the  Russian  name.     ■ 
