554  PKE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
been  several  periods  of  eruption  of  trap  dikes,  as  is  shown  by  the 
manner  in  which  they  cut  one  another. 
Jackson,9  in  1844,  gives  many  facts  as  to  the  distribution  of  the 
rocks,  with  numerous  sectional  profiles.  Granite,  syenite,  porphyry, 
trap,  basalt,  and  lava  are  regarded  as  eruptive  rocks.  As  a  result  of 
outbursts  and  elevations  the  strata  have  been  broken  up,  altered  in  po- 
sition, and  included  between  masses  of  molten  gneiss  and  granite.  In 
this  way  is  explained  the  intercalation  of  masses  of  argillaceous  slates 
in  the  Primary  series  and  the  metamorphism  of  the  sedimentary  de- 
ix>sits  by  igneous  action. 
Kogers  (H.  D.  and  W.  B.),10  in  184G,  state  that  the  assumption 
that  the  White  Mountains  belong  to  the  Primary  series  involves  two 
errors:  First,  in  assigning  all  the  rocks  to  the  gneissoid  class;  and, 
second,  in  supposing  that  none  of  the  strata  contain  organic  remains. 
The  gorge  of  the  Saco  was  closely  examined.  The  rocks  were  found 
to  have  a  stratified  structure  throughout,  although  in  many  cases  ap- 
proaching very  close  to  granite.  They  are  regarded  as  very  highly 
metamorphic  sandstones  and  slates.  Associated  with  the  crystalline 
rocks  are  semicrystalline  sandstones  which  contain  distinct  frag- 
ments. In  a  shale  are  found  fossils  which  lead  to  the  conclusion  that 
the  series  represents  the  Levant  or  Matinal.  The  metamorphic  beds 
are  cut  by  beds  and  veins  of  syenitic  granite,  and  the  extremely 
crystalline  character  of  the  slates  and  sandstones  is  regarded  as  due 
to  the  igneous  material. 
Jackson,11  in  1848,  maintains  that  in  the  White  Mountains  are 
numerous  localities  where  the  granite  contains  fragments  of  slate 
which  are  not  altered  by  heat  beyond  mere  induration.  In  New 
Hampshire  numerous  masses  of  older  Silurian  strata  occur  inter- 
calated with  the  Primary  rocks. 
Hitchcock  (C.  H.)  and  Huntington,12  in  1877,  give  a  full  account 
of  the  geology  of  Xew  Hampshire.  Hitchcock  divides  the  pre- 
Paleozoic  rocks  of  northeastern  United  States  into  two  divisions: 
First,  the  more  ancient  gneisses  and  granites;  second,  the  area  of  hy- 
dromicaceous  and  micaceous  schists,  which  are  termed  Huronian.  In 
the  Paleozoic  are  placed  great  expanses  of  clay  slates.  The  first  division 
is  divided  into  four  parts:  First  and  oldest,  the  Laurentian;  second, 
the  porphyritic  gneiss  and  the  various  undetermined  granites ;  third, 
the  Atlantic,  and  fourth,  the  Labradorian.  Among  the  Huronian  is 
placed  the  Quebec  group  of  Logan. 
Huntington  gives  the  geology  of  the  Coos  and  Essex  district.  The 
Coos  rocks,  consisting  of  argillaceous  schists,  clay  slates,  and  mica- 
ceous sandstones,  are  supposed  to  belong  to  the  fossiliferous  series. 
The  Huronian  rocks  are  found  east  of  the  line  limiting  the  Coos 
group.  They  consist  of  green  chloritic  rocks,  in  which  the  lines  of 
stratification  are  obscure.     Included  are  greenish  feldspathic  sand- 
