434  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
Character  of  the  deposits. — Until  recently  all  the  materials  of  the  cape  have  been  consi  J 
ered  to  have  been  deposited  in  connection  with  the  ice  which  covered  the  region  in  tl 
fast  or  Wisconsin  glacial  stage.  It  is  now  known,  however,  that  these  Wisconsin  deposit 
including  those  of  the  moraine  and  outwash  plain,  are  relatively  thin  and  superficial,  tl 
mass  of  the  materials  being  made  up  of  a  complex  succession  of  beds  of  different  type  1 
most  of  which  are  far  older  than  those  of  the  last  ice  invasion.  These  deposits,  whic 
belong  to  a  series  extending  from  New  York  Harbor  eastward  to  the  locality  under  di; 
cussion  have  been  carefully  studied  on  Long  Island,  New  York,  and  at  other  points  alon 
the  coast,  and  their  sequence  has  been  determined.  The  succession  and  character  of  thos 
which  occur  above  sea  level  or  which  approach  close  to  that  level  on  the  cape  are  show 
in  the  foregoing  table. 
OCCURRENCE  OF  THE  CLAYS. 
From  the  foregoing  table  it  will  be  seen  that  there  are  four  clays  represented  in  th 
materials  making  up  Cape  Cod.  Only  the  Gardiner  clay  and  the  clayey  phases  of  tin 
Jacob  and  Montauk  formations,  however,  are  known  to  occur  above  sea  level,  hence  it  i: 
with  them  alone  that  the  present  discussion  deals.  The  thick  Cretaceous  clays  which  an 
the  foundation  for  many  of  the  great  clay  industries  of  New  Jersey  and  elsewhere  an 
unfortunately,  so  far  as  known,  below  sea  level  on  Cape  Cod.  They  are  probably  lost 
than  50  feet  below  tide  level  at  Highland  Light,  to  judge  from  the  low  horizon  of  the  glacia 
deposits  exposed  at  the  base  of  the  bluff,  and  it  is  possible  thai  they  rise  above  sea  leve 
in  the  inland  portion  of  the  cape  in  the  North  Truro  region,  possibly  even  appearing  neai 
the  bottom  of  the  deeper  valleys,  although  no  such  clays  have  yet   been  reported. 
COMPOSITION   AND   STRUCTURE   OF  THE  CLAYS, 
Chanutti  of  tin  Gardiner  clay.  The  best  exposure  of  the  Gardiner  clay  is  in  the  bluff 
at  Highland  Light,  Truro,  where  it  has  a  thickness  of  about  10  feet.  It  is  a  very  tough, 
not  very  plastic  clay,  varying  from  dark  gray  to  dull  black  in  color.  The  latter  variety 
is  most  frequently  seen  in  the  lower  part  of  the  bed  and  the  lighter  gray  variety  in  the 
upper  part.  The  top  is  sometimes  colored  a  dull  grayish  to  greenish  brown,  this  being 
due,  it  is  thought,  to  the  action  of  percolating  waters  passing  along  the  contact  of  the 
clay  at  the  base  of  the  loose  overlying  sands.  The  whole  is  minutely  laminated,  although 
this  structure  is  not  always  clearly  visible  excepl  on  exposed  edges  etched  out  by  the 
atmosphere.  The  lighter-colored  type,  of  clay  may  show  a  distinct  though  not  strongly 
developed  shaly  structure,  apparently  due  to  the  presence  of  thin  lamina'  of  very  line 
sand.  An  occasional  quartz  pebble  up  to  one-fourth  inch  or  so  in  diameter  may  occur, 
but  no  granitic  pebbles  or  layer-  of  quartz  pebbles  have  been  seen.  The  clay  does  not. 
appear  to  contain  much  true  kaolin,  being  rather  a  quartz  Hour.  \o  fossils,  lignite,  or 
other  traces  of  organic  life  have  been  seen. 
The  Highland  Light  deposit  may  be  taken  as  a  type  of  the  Gardiner  clay  in  this  region. 
Nowhere  else,  however,  does  it  attain  such  a  development,  being  ordinarily  much  thinner, 
the  thickness  being  perhaps  as  low  as  5  feel  in  some  places,  while  in  others  the  clay  may 
even  have  been  entirely  removed  by  the  Montauk  ice.  lis  character  is  fairly  constant 
throughout  the  region,  although,  because  of  local  conditions  more  favorable  to  weather- 
ing, the  brown  phase  is  often  more  conspicuous  than  at  Highland  Light.  In  the  bluff 
sections,  where  it  has  been  longer  exposed  to  the  action  of  the  weather,  the  clay  often 
appears  structureless  and  may  crumble  into  the  small  pellets  described  in  other  parts  of 
the  country  as  "buckshot." 
Character  of  the  clays  of  the  Jacob  formation. — In  mosl  localities  where  the  Gardiner  ciay 
is  exposed,  and  intervening  between  it  and  the  coarser  materials  of  the  Herod  formation, 
are  transitional  beds  of  fine  material  varying  from  sandy  clays  to  clayey  sands.  The  more 
clayey  phases  approach  the  clays  of  the  Gardiner  in  composition,  the  only  difference  being 
the  presence  of  a  larger  percentage  of  sandy  laminae.  At  other  times  the  Jacob  is  much 
coarser,  in  which  case  the  contact  with  the  Gardiner  clays  is  quite  definite.     In  color  the 
