664  PKE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
HIGHLAND  BELT.a 
The  geology  of  the  Highland  belt,  worked  out  for  New  Jersey, 
doubtless  extends  southwest  into  the  Pennsylvania  Highland  belt. 
No  recent  detailed  mapping  has  been  done  here.  The  rocks  are  de- 
scribed by  Lesley  as  a  complex  of  syenite,  granite,  granulite,  horn- 
blende schist,  mica  schist,  magnetic  iron  ore,  and  hornblende  gneiss, 
lacking  the  crystalline  limestone  beds  characteristic  of  the  New  Jersey 
Highlands. 
SOUTH    MOUNTAIN    OF    PENNSYLVANIA.0 
As  shown  by  the  work  of  Walcott,  Williams,  Keith,  and  Bascom, 
the  oldest  rocks  in  South  Mountain  of  Pennsylvania  are  felsites  and 
basalts,  the  former  being  predominant.  Both  of  these  vary  from 
compact  to  amygdaloidal,  and  are  accompanied  by  tuffs  and  breccias. 
The  volcanics  have  been  extensively  transformed  into  slates  and 
schists  by  dynamic  action.  These  are  unconformably  overlain  by 
quartzite  conglomerates  and  sandstones,  or  by  shales,  which  bear  the 
Olenellus  fauna. 
It  therefore  follows  that  the  volcanic  rocks  of  South  Mountain 
are  pre-Cambrian,  but  as  yet  no  evidence  is  available  to  give  them 
a  more  definite  place  than  this. 
SECTION  2.    MARYLAND     AND    ADJACENT     PORTIONS     OF 
VIRGINIA  AND  PENNSYLVANIA. 
SUMMARY  OF  LITERATURE. 
Ducatel  and  Alexander,22  in  1834,  describe  the  Primary  rocks  as 
one  of  the  chief  divisions.  These  include  the  following  formations: 
Granite,  gneiss,  limestone,  and  serpentine. 
Aikin,23  in  1834,  states  that  granite  and  Primitive  schists  are  inter- 
mingled in  every  possible  manner  in  the  region  west  of  Baltimore, 
the  dips  being  with  a  good  deal  of  regularity  toward  the  southeast. 
Succeeding  the  Primitive  rocks  are  Transition  slates,  sandstones, 
limestones,  and  graywackes  interstratified  with  Transition  limestones. 
Ducatel,24  in  1839,  states  that  the  limestones  of  Harford  and  Bal- 
timore counties  occur  in  the  valleys.  In  the  northwestern  part  of 
these  counties  the  rocks  are  argillites,  which  pass  into  talcose  slates, 
and  these  are  succeeded  by  granitic  aggregates  in  which  hornblende  is 
the  prevailing  rock. 
Tyson,25  in  1860,  classifies  the  rocks  of  Maryland  into  those  of  igne- 
ous and  aqueous  origin.  In  the  former  are  granite,  syenite,  massive 
quartzite,  porphyry,  amygdaloid,  trap  (including  hornblende  rock  or 
amphibolite),  and  serpentine.     The  rocks  of  aqueous  origin  include 
°  By  the  authors. 
