350  PRE-CAMBRIAN   ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
are  found  superimposed  upon  each  other,  although  there  are  at  least  a 
half  dozen  series  which  are  regarded  as  representing  different  parts  of 
the  geological  section.  The  aggregate  thickness  of  the  various  sections 
is  not  less  than  6,000  feet  and  may  be  one  half  more  than  this.  The 
great  part  of  mount  Desert  rocks  are  referred  to  the  lower  part  of  the 
Cambrian  section,  although  the  volcanic  rocks  of  Cranberry  island 
resemble  deposits  of  similar  nature  at  Eastport,  Maine,  which  seem  to 
be  of  Silurian  age. 
to 
LITERATURE  OF  NEW  HAMPSHIRE. 
Jackson,9  in  1841,  in  a  general  consideration  of  the  geology  of  the 
state,  states  that  granite  is  an  igneous  rock  and  is  the  foundation  on 
which  all  the  more  recent  formations  rest.  When  it  is  found  cutting 
other  rocks,  the  intense  heat  has  often  metamorphosed  the  adjacent 
rocks  for  considerable  distances.  Eeposing  directly  on  the  granite  is 
found  gneiss,  the  origin  of  which  is  undetermined.  By  some  geologists 
gneiss  is  considered  a  metamorphic  rock;  others  suppose  that  its  strat- 
ified structure  is  due  to  the  crystallization  in  laminse  and  that  it  is 
merely  the  upper  crust  of  granite.  Above  the  gneiss  are  found  mica- 
slate,  chlorite- slate,  and  argillaceous  slate,  which  are  regarded  as 
metamorphic  rocks.  Slates  and  granite  alternate  with  each  other,  and 
this  is  due  to  the  subsequent  intrusion  of  granite.  There  have  been 
several  periods  of  eruptions  of  trap  dikes,  as  is  shown  by  the  manner 
in  which  they  cut  each  other. 
Jackson,10  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  out- 
bursts 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  metamorphosis  of  the  'sedimentary  depos- 
its by  igneous  action. 
Bogers,  (Henry  D.  and  Wm.  B.),11  in  1846,  state*  that  the  assump- 
tion 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  fragments. 
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. 
