ADIRONDACK    MOUNTAINS.  607 
coarsely  crystalline,  usually  graphitic,  and  often  include  silica 
from  little  scales  to  large  bunches.  At  Keene  Center,  in  the  heart  of 
the  Adirondacks,  is  a  white  limestone  and  schist  belt  which  contains 
magnetic  iron  ore  and  is  overlain  by  garnetiferous  and  pyroxenic 
schists  or  pyroxenic  granulite,  the  relations  indicating  that  the  latter 
is  a  gneissic  rock  interbedded  with  the  limestone. 
There  is  no  marked  break  to  be  detected  anywhere  between  the 
gneiss  and  the  overlying  limestone.  Apparently  the  whole  is  a  con- 
tinuous series  of  strata,  which  are  analogous  in  appearance  with  those 
of  the  Grenville  series  of  Canada.  It  therefore  does  not  appear  cer- 
tain that  in  the  eastern  Adirondack  region  there  are  any  rocks  older 
than  this  series.  The  extent  and  persistence  of  the  limestones  and 
schists  give  ground  for  believing  that  the  series  was  a  set  of  calca- 
reous sediments  and  sandstones  which  have  been  metamorphosed  and 
intruded  by  the  anorthosites. 
Darton,35  in  1895,  describes  and  maps  the  faulted  region  of  Her- 
kimer, Fulton,  Montgomery,  and  Saratoga  counties,  N.  Y.  Lauren- 
tian  rocks  occupy  the  northern  part  of  the  area,  forming  the  floor  for 
a  succession  of  sandstones,  limestones,  and  shales,  which  dip  to  the 
south  at  a  very  moderate  angle. 
Cushing,36  in  189G,  argues  for  the  existence  of  pre-Cambrian  as 
well  as  post-Ordovician  dikes  in  the  Adirondacks  and  along  Lake 
Champlain,  offering  the  following  reasons:  (1)  A  much  larger  num- 
ber of  dikes  occur  in  the  pre-Cambrian  than  in  the  Paleozoic  rocks. 
(2)  A  great  proportion  of  the  dikes  are  of  diabase,  while  diabase 
rocks  are  not  found  outside  of  the  pre-Cambrian  areas.  (3)  Along 
the  line  of  contact  of  the  Potsdam  with  the  older  rocks  north  of  the 
Adirondack's  the  plentiful  diabase  dikes  in  the  older  rocks  are  appar- 
ently cut  off  by  the  Potsdam. 
Kemp,87  in  1897,  describes  the  geology  of  the  magnetites  near  Port 
Henry,  N.  Y.,  and  especially  those  of  Mineville,  in  the  Adirondacks 
of  New  York.  The  oldest  rocks  present  in  the  district  are  quartzose 
gneisses  and  white  crystalline  limestones,  with  perhaps  some  more 
basic  gneisses.  The  limestones  appear  to  lie  largely  in  the  upper  part 
of  this  group,  but  some  of  them  are  certainly  below  the  other  mem- 
bers. The  acidic  gneisses  may  have  been  granites  or  quartz  diorites. 
The  gneiss  and  limestone  group  is  cut  by  anorthosite  intrusives.  and 
both  are  in  turn  cut  by  gabbro  intrusive-.  Trap  dikes,  usually  of 
small  width,  are  very  common  in  this  district.  The  age  of  these  dike- 
is  undetermined,  but  it  seems  probable  that  they  may  be  of  two  ages. 
pre-Potsdam  and  post-Utica.  Overlying  unconformable  all  of  the 
above-described  rock-  is  the  Pot-dam  sand-tone. 
Kemp,38  in  1898,  continue-  his  preliminary  report  on  the  geology 
of  Essex  County.  X.  Y.,  with  an  account  of  the  detail  geology 
of  the  individual  town-hips.     The  additional  observations  have  cor- 
