PIEDMONT  PLATEAU  AND  PORTIONS  OF  THE  APPALACHIANS.      655 
mon,  which  is  regarded  as  proving  that  the  metamorphism  is  due  to 
heated  gases  rising  through  fissures  rather  than  to  the  contact  of  ig- 
neous material. 
The  Primal  southern  belt  is  first  considered.  At  Attleboro  there 
is  no  marked  discordance  between  this  and  the  gneissic  series  which 
is  supposed  to  be  older.  East  of  the  Schuylkill  and  in  Montgomery 
County  the  observer  is  very  liable  to  confound  the  lowest  Primal  beds 
with  the  uppermost  hornblendic  feldspathic  layers  of  the  adjacent 
genuine  gneiss.  West  of  the  Schuylkill  the  Primal  slates  are  of  so 
crystalline  a  character  that  it  is  sometimes  difficult  to  distinguish  the 
strata  from  certain  forms  of  the  more  micaceous  beds  of  the  true 
gneissic  or  Hypozoic.  It  is  impossible  to  subdivide  the  members  of 
the  lower  Primal  group  in  southern  Pennsylvania,  because  of  a  pre- 
vailing transverse  cleavage,  which  extensively  effaces  all  clear  traces 
of  the  original  bedding;  because  of  the  presence  of  innumerable 
plications,  often  so  closely  compressed  as  to  appear  as  only  one  uni- 
form dip,  the  anticlinal  and  synclinal  foldings  in  many  cases  escaping 
detection  through  the  obscuring  influence  of  cleavage ;  and  because  of 
mutations  in  the  composition  of  the  beds.  The  rocks  between  the 
Primal  white  sandstone  and  the  genuine  gneiss  then  include  talcoid 
siliceous  slate,  talco-micaceous  slate,  and  schistose  and  quartzose 
micaceous  rock.  On  the  Brandywine  the  massive  gneisses  and  finely 
laminated  material  are  interlaminated  in  such  a  way  as  to  lead  to  the 
conclusion  that  the  latter  are  closely  infolded  in  the  older  meta- 
morphic  series.  In  the  Primal  of  Susquehanna  and  York  counties  the 
true  bedding  is  very  obscure,  being  almost  obliterated. 
In  going  southward  along  the  Susquehanna  one  finds  the  rocks 
becoming  steadily  more  crystalline,  until  they  are  so  altered  as  to 
have  been  hitherto  mistaken  for  the  true  Hypozoic.  The  precise  line 
of  contact  of  the  limestones  with  the  slates  is  not  clearly  visible  at 
times;  indeed,  there  seems  to  be  no  line  of  sudden  transition.  The 
cleavage  planes  are  in  general  parallel  with  those  of  the  original  bed- 
ding. The  dips  on  this  river  are  steadily  in  a  southeast  direction  for 
a  distance  of  7  or  7i  miles,  and  it  is  believed  that  the  rocks  consist 
of  many  compressed  folds  which  repeat  the  same  strata  many  times. 
Southwest  of  the  Susquehanna,  in  the  South  Mountains,  in  Adams, 
Cumberland,  and  Franklin  counties,  is  an  extensive  area  which  is 
placed  with  the  Primal  series.  It  is  a  continuation  of  the  Blue  Ridge 
of  Maryland  and  Virginia.  There  are  a  few  intrusive  rocks,  mostly 
of  greenstone  and  trap.  Some  of  the  rocks  are  very  crystalline,  but 
none  are  regarded  as  belonging  to  the  gneissic  series.  In  this  series 
are  found  limestones  associated  with  iron  ore. 
Leeds,4  in  1870,  states  that  on  the  Germantown  Railroad,  3  miles 
from  Philadelphia,  in  the  micaceous  schists  are  embedded  huge  bowl- 
ders of  hard,  compact,  hornblende  rock.    They  are  supposed  to  be  a 
