CHAPTER  XL 
PIEDMONT  PLATEAU  AND  ADJACENT  PORTIONS  OF 
THE  APPALACHIANS  IN  ALABAMA,  GEORGIA,  TEN- 
NESSEE, NORTH  CAROLINA,  SOUTH  CAROLINA,  VIR- 
GINIA, MARYLAND,  PENNSYLVANIA,  AND  DELAWARE. 
SSCTIOX  1.     PENNSYLVANIA. 
SUMMARY  OF  LITERATURE. 
Finch,1  in  182-1,  finds,  near  Easton,  s}Tenite,  serpentine,  and  Transi- 
tion limestone,  Transition  granite,  Transition  clay  slate,  and  Transi- 
tion sandstone. 
Finch,2  in  1828,  finds  a  section  from  Chads  Fork  to  Westchester  to 
include  gneiss,  mica  slate,  hornblende  slate,  Primitive  sandstone,  and 
Transition  quartz  rock. 
Rogers  (H.  D.),3  in  1858,  gives  a  systematic  account  of  the  meta- 
morphic  rocks  of  Pennsylvania.  These  are  divided  into  three  main 
divisions — the  gneissic  series  proper,  or  Hypozoic;  Azoic,  or  those 
destitute  of  relics  of  life,  and  Paleozoic.  The  Hypozoic  rocks  only 
are  placed  with  the  Primary.  The  Azoic  schists  are  regarded  as 
newer  than  the  Hypozoic,  because  of  differences  in  the  position  of 
the  two  sets  of  strata,  in  condition  of  metamorphisni,  and  in  manner 
of  plication.  The  former  dip  almost  invariably  to  the  southeast, 
while  the  gneiss  in  many  localities  has  no  symmetrical  folding.  These 
dissimilarities  imply  essential  differences  in  the  directions  and  dates 
of  the  crust  movements.  The  Azoic  rocks,  however,  when  they  show 
the  maximum  amount  of  metamorphisni,  simulate  in  mineral  aspect 
and  structure  those  of  the  gneissic  series.  The  old  strata  are  then 
sepa rated  into  three  systems  by  two  main  horizons,  the  lower,  a 
physical  break  between  the  Hypozoic  and  the  Azoic;  the  upper,  a  life 
limit  denoting  the  first  advent,  so  far  as  discovered,  of  organic  beings. 
The  gneissic  rocks  are  separated  structurally  into  three  districts: 
First,  the  area  running  southwestward  from  Trenton,  through  Phila- 
delphia; second,  the  area  between  the  Schuylkill  and  the  Susque- 
hanna, north  of  the  firsl  area:  and.  third,  the  South  Mountain  region. 
a  continuation  of  the  Highlands  of  New  Jersey.  The  Philadelphia 
belt  is  intersected  very  extensively  by  eruptive  rocks,  such  as  granite. 
greenstone,  syenite,  and  trap.  The  second  or  middle  licit  is  sometimes 
called  the  mica  schist  belt,  because  of  the  amount  of  this  mineral 
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