﻿H. 
  E. 
  Gregory 
  — 
  Andesites 
  from 
  Maine. 
  369 
  

  

  Art. 
  XLIII. 
  — 
  Andesites 
  of 
  the 
  Aroostoolt 
  Volcanic 
  Area 
  of 
  

   Maine 
  ;^ 
  by 
  Herbert 
  E. 
  Gregory. 
  

  

  Andesites 
  are 
  rare 
  rocks 
  in 
  the 
  eastern 
  United 
  States, 
  but 
  

   are 
  the 
  most 
  abundant 
  extrusives 
  so 
  far 
  found 
  in 
  northern 
  

   Maine. 
  They 
  form 
  prominent 
  hills 
  and 
  determine 
  the 
  general 
  

   topography 
  in 
  some 
  places, 
  while 
  in 
  others 
  they 
  are 
  represented 
  

   by 
  isolated 
  remnants 
  among 
  the 
  sedimentaries. 
  The 
  greater 
  

   number 
  of 
  occurrences 
  are 
  of 
  lava 
  and 
  breccia, 
  but 
  andesitic 
  

   ash 
  and 
  tuif 
  are 
  also 
  found 
  well 
  developed. 
  In 
  the 
  following 
  

   descriptions 
  only 
  the 
  more 
  inaportant 
  localities 
  will 
  be 
  dealt 
  

   with 
  in 
  detail. 
  The 
  andesites 
  are 
  located 
  in 
  Aroostook 
  County 
  

   in 
  the 
  townships 
  of 
  Chapman, 
  Mapleton, 
  and 
  Castle 
  Hill, 
  

   where 
  they 
  constitute 
  prominent 
  ridges, 
  known 
  as 
  Edmund's 
  

   Hill, 
  Hobart 
  Hill 
  and 
  Castle 
  Hill, 
  and 
  several 
  less 
  noticeable 
  

   masses. 
  

  

  Field 
  Description. 
  

  

  Edmund'' 
  s 
  Hill 
  Andesites. 
  — 
  Edmund's 
  Hill 
  is 
  situated 
  in 
  

   Chapman 
  township 
  near 
  the 
  middle 
  of 
  the 
  north 
  township 
  

   line, 
  and 
  is 
  simply 
  the 
  highest 
  part 
  of 
  a 
  ridge 
  running 
  JST.-S. 
  

   for 
  several 
  miles. 
  The 
  hill 
  itself 
  rises 
  some 
  200 
  feet 
  above 
  the 
  

   road 
  at 
  its 
  base 
  and 
  presents 
  the 
  outline 
  of 
  a 
  drumlin 
  — 
  so 
  

   evenly 
  has 
  it 
  been 
  graded 
  at 
  each 
  end. 
  The 
  trees, 
  brush, 
  talus, 
  

   and 
  glacial 
  deposits 
  entirely 
  conceal 
  the 
  formations 
  about 
  the 
  

   base 
  of 
  the 
  hill, 
  and 
  it 
  is 
  only 
  after 
  climbing 
  half 
  the 
  distance 
  

   to 
  the 
  top 
  that 
  the 
  bare 
  rock 
  is 
  found 
  in 
  place. 
  In 
  climbing 
  

   up 
  the 
  west 
  side 
  of 
  the 
  hill 
  fragments 
  of 
  fossiliferous 
  sandstone 
  

   were 
  found 
  amongst 
  the 
  andesite 
  blocks, 
  and 
  about 
  100 
  feet 
  

   below 
  the 
  top 
  the 
  sandstone 
  ledge 
  outcrops. 
  The 
  thickness 
  

   and 
  extent 
  of 
  the 
  sandstone 
  could 
  not 
  be 
  determined 
  accurately 
  

   because 
  covered 
  in 
  so 
  many 
  places 
  with 
  heavy 
  blocks 
  and 
  

   small 
  fragments 
  of 
  the 
  igneous 
  rock 
  fallen 
  down 
  from 
  above. 
  

   The 
  contact 
  was 
  not 
  seen. 
  The 
  entire 
  top 
  of 
  the 
  hill 
  is 
  of 
  

   augite-andesite. 
  The 
  main 
  mass 
  is 
  uniform 
  in 
  texture 
  and 
  cut 
  

   by 
  cleavage 
  cracks 
  into 
  large 
  blocks, 
  which, 
  when 
  they 
  fall 
  

   down 
  the 
  slope, 
  remain 
  as 
  huge 
  masses. 
  The 
  south 
  and 
  north 
  

   ends, 
  however, 
  and 
  part 
  of 
  the 
  west 
  side 
  are 
  quite 
  different. 
  

   Here 
  the 
  rock 
  is 
  split 
  up 
  into 
  long, 
  thin 
  slabs 
  by 
  a 
  set 
  of 
  par- 
  

   allel 
  cracks 
  remarkably 
  uniform 
  in 
  direction 
  and 
  length, 
  and 
  

   they 
  retain 
  their 
  parallelism 
  even 
  when 
  the 
  rock 
  is 
  folded 
  or 
  

   faulted. 
  Cross 
  cleavages 
  intersect 
  these 
  cracks 
  every 
  few 
  feet, 
  

  

  * 
  A 
  portion 
  of 
  a 
  thesis 
  on 
  the 
  " 
  Geology 
  of 
  the 
  Aroostook 
  volcanic 
  area 
  of 
  

   Maine 
  " 
  presented 
  for 
  the 
  doctorate 
  degree 
  at 
  Yale 
  University 
  in 
  1899. 
  The 
  full 
  

   report 
  will 
  appear 
  later 
  as 
  a 
  publication 
  of 
  the 
  U. 
  S. 
  Geological 
  Survey, 
  to 
  which, 
  

   under 
  the 
  direction 
  of 
  Prof. 
  H. 
  S. 
  Williams, 
  the 
  author 
  owes 
  the 
  opportunity 
  of 
  

   making 
  the 
  investigations 
  here 
  recorded. 
  

  

  