ADIRONDACK    MOUNTAINS.  613 
and  most  scattered.  From  the  presence  of  the  quartzites  it  is  inferred 
that  clastic  sediments  must  have  been  present  in  larger  amounts  than 
lias  heretofore  been  realized.  On  the  east  it  has  not  been  proved  that 
sediments  form  synclines  pinched  into  the  underlying  gneissoid  rocks; 
on  the  contrary,  they  seem  to  constitute  Low-dipping,  flat  monoclines. 
Kemp,49  in  1900,  describes  and  maps  the  geology  of  the  Lake.  Placid 
region  in  the  Adirondacks,  in  the  northwestern  part  of  Essex  County. 
Crystalline  rocks  of  Algonkian  age  occupy  a  large  part  of  the  area. 
These  include  crystalline  limestone,  quartzite,  granite,  gneiss,  and 
anorthosite.  It  is  probable- that  some  of  the  gneisses,  especially  those 
associated  with  the  limestones  and  quartzites,  are  altered  sediments, 
and  it  is  also  probable  that  the  gneisses  with  augen  of  labradorite  are 
squeezed  igneous  rocks,  but  the  investigation  does  not  permit  of  their 
separation.  The  anorthosites  have  intruded  and  metamorphosed  the 
limestones  and  quartzites,  and  probably  some  of  the  gneisses.  It  has 
been  noted  that  the  anorthosite  frequently  passes  outward  by  gradual 
transition  into  the  dark  gneisses  with  labradorite  augen.  Cutting  all 
the  above  rocks  are  trap  dikes,  but  whether  pre-Cambrian  or  later  is 
unknown. 
Smyth  and  Newland,50  in  1900,  report  progress  in  the  mapping 
of  the  crystalline  rocks  of  the  western  Adirondack  region.  Inclu- 
sions of  hornblende  schist  found  in  the  more  acidic  gneisses  of  the 
region  are  believed  to  afford  important  evidence  as  to  the  origin  of 
the  gneisses.  Also  light-red  granitoid  gneiss  has  been  found  intru- 
sive into  a  gray  gneiss,  indicating,  as  before  held,  that  all  the  gneisses 
are  not  of  the  same  age.  Certain  of  the  gneisses  are  found  to  be 
younger  than  and  intrusive  into  certain  schists  associated  with  the 
limestones. 
KEMr,  Newland,  and  Hill/'1  in  1900,  further  discuss  the  geology 
of  Hamilton,  Warren,  and  Washington  counties,  extending  the  ob- 
servations noted  in  previous  reports  to  the  west  and  south.0  The 
additional  points  of  interest  are  the  occurrence  of  anorthosites  in 
Johnsburg,  in  Warren  County,  the  southernmost  exposure  yet  known 
in  the  eastern  mountains,  and  the  increasing  certainty  of  the  existence 
of  sedimentary  gneisses  in  Fort  Ann  and  Johnsburg  townships. 
Cushing,52  in  1900,  describes  and  maps  the  pre-Cambrian  rocks  of 
Franklin  County,  X.  Y.  These  are  classified  as  Grenville  (Algon- 
kian) rocks,  igneous  rocks  intrusive  in  the  Grenville,  and  other 
igneous  rocks  of  doubtful  age,  possibly  in  part  older  than  the  Gren- 
ville rocks. 
The  Grenville  rocks  occur  in  small  disconnected  patches  surrounded 
by  intrusive  igneous  rocks.     Some  of  them  have  such  position  with 
aFor  general  discussion  of  classification  of  geology  of  these  counties  see  Seventeenth 
Ann.  Kept.  New  York  State  Geologist,  Eor  1897,  published  in  Fifty-flrsl  Ann.  Kept.  New 
York  State  Museum,  vol.  2,   L899,  pp.  499-553. 
