van  Hisfi.]  EASTERN    UNITED    STATES.  407 
17,000  feet  of  quartzite  and  sandy  shale  and  about  2,000  feet  of  chloritio 
slates.  In  another  section  the  rocks  observed  are  quartz-conglomer- 
ate-schist, jaspery  quartzites,  crystalline  schists,  and.  orthofelsites. 
The  relations  seem  to  show  an  unconform ability  between  the  older 
(Huronian?)  orthofelsites  and  schists  and  the  more  recent  (Cambrian'?) 
sandstone,  but  it  would  seem  additionally  to  imply  that  the  alignment 
of  the  one  system  was  the  result  of  causes  entirely  different  from  and 
anterior  to  those  that  formed  the  other.  In  another  section  the  rocks 
increase  in  felsitic  character  to  the  southeast  and  in  conglomeratic 
schistose  character  to  the  northwest.  It  is  concluded  that  the  South 
mountain  chain  is  composed  of  two  groups  of  rocks,  the  lower  consist- 
ing of  quartz -conglomerates  in  which  quartzite  occurs;  the  upper  fel- 
sitic in  character,  containing  hydro-mica  schists  and  chlorite- schists. 
The  felsite  itself  ranges  from  a  sandy  slate  to  a  coarsely  porphyritic 
rock. 
Hunt,152  in  1877,  states  that  near  Oonshohocken  is  a  belt  of  Lauren- 
tian  gneiss  identical  with  that  of  the  South  and  Welsh  mountains,  that 
separates  the  Philadelphia  gneisses  and  mica-schists,  which  are  Mont- 
alban,  from  the  Auroral  limestone.  The  Laurentian  gneiss  is  succeeded 
on  the  northeast  by  serpentines,  chloritic  schists,  micaceous  schists, 
and  argillites,  which  are  typical  Huronian  rocks.  The  intermediate 
position  of  the  Huronian  seems  to  show  that  it  is  below  the  Montalban. 
The  Primal  and  Auroral  are  the  Lower  Taconic  of  Emmons.  South  of 
the  Susquehanna,  South  mountain  rocks  again  appear  and  stretch 
southward  to  the  Potomac.  They  here  consist  of  Montalban  and  Huron- 
ian rocks.  In  the  southern  part  of  Pennsylvania  are  bedded  petrosilex 
rocks,  often  jasper-like,  which  are  associated  with  characteristic  rocks 
of  the  Huronian  series,  to  which  they  are  all  referred. 
Prime,157  in  1878,  describes  gneiss  and  mica-schist  in  Lehigh  county 
as  Laurentian.  A  little  west  of  Seller's  quarry  the  Potsdam  sandstone 
and  Laurentian  rocks  are  seen  in  contact.  The  dips  of  the  two  seem 
to  be  conformable,  but  this  may  be  wrong,  as  the  exposure  is  small  and 
the  gneiss  apparently  has  a  slight  roll.  The  gneissic  rock  is  here  dis- 
tinctly bedded. 
Frazer,154  in  1880,  includes  in  the  post-Eozoic  series  of  Lancaster 
county  calcareous  argillites,  nacreous  slates,  hydro-mica- schists,  chikis 
quartzite,  and  chloritic  series.  In  the  Eozoic  series  is  placed  the 
mica-schist  and  gneiss  belt.  Between  this  series  and  the  previous  one 
there  is  no  certain  evidence  of  nonconformability,  the  transition  from 
one  rock  to  the  other  being  gradual  and  the  line  between  them  difficult 
to  define. 
Frazer,155  in  1880,  states  that  the  chloritic  series  p*ass  into  the  Peach 
bottom  slates  within  a  breadth  of  a  few  hundred  yards,  and  equally 
abruptly  into  chlorites  again,  and  finally  into  greenish  chloritic  quartz- 
ite, in  all  respects  like  those  of  the  South  mountain.  If  the  Peach 
bottom  slates  are  Hudson  river  age  as  supposed ,  a  difficulty  is  here 
presented. 
