﻿H. 
  E. 
  Gregory 
  — 
  Andesites 
  from 
  Maine. 
  367 
  

  

  of 
  chlorite, 
  with 
  parallel 
  extinction 
  and 
  a 
  pleochroism, 
  c 
  = 
  

   white 
  green, 
  a 
  = 
  brown 
  green. 
  At 
  times 
  the 
  former 
  crystal 
  is 
  

   striped 
  across 
  with 
  alternating 
  bands 
  of 
  green 
  and 
  white 
  in 
  the 
  

   direction 
  of 
  the 
  cleavage 
  cracks. 
  Some 
  of 
  the 
  crystals 
  classed 
  

   as 
  hornblende 
  are 
  so 
  altered 
  that 
  it 
  is 
  impossible 
  to 
  say 
  that 
  

   they 
  may 
  not 
  be 
  angite. 
  

  

  The 
  groiindmass 
  is 
  formed 
  of 
  small, 
  stringy, 
  ragged 
  feld- 
  

   spars 
  and 
  varies 
  in 
  different 
  slides 
  from 
  trachytic 
  or 
  pilotaxitic, 
  

   with 
  possibly 
  a 
  little 
  glass, 
  to 
  a 
  type 
  formerly 
  quite 
  glassy 
  and 
  

   showing 
  devitrified 
  areas 
  with 
  incipient 
  micropoikilitic 
  struc- 
  

   ture. 
  The 
  feldspar 
  microlites 
  could 
  not 
  be 
  accurately 
  deter- 
  

   mined, 
  but 
  their 
  average 
  extinction 
  indicates 
  a 
  variety 
  as 
  acid 
  

   as 
  oligoclase-andesine, 
  and 
  if 
  strict 
  nomenclature 
  were 
  to 
  be 
  

   considered, 
  the 
  rock 
  would 
  be 
  classed 
  as 
  a 
  trachyte-andesite. 
  

  

  Andesites 
  of 
  Southern 
  2Lapleton. 
  — 
  These 
  occur 
  in 
  several 
  

   localities 
  and 
  are 
  either 
  identical 
  with, 
  or 
  present 
  only 
  minor 
  

   variations 
  from, 
  the 
  Edmund's 
  Hill 
  and 
  Hobart's 
  Hill 
  masses. 
  

   The 
  rock 
  which 
  outcrops 
  in 
  the 
  road 
  two 
  miles 
  east 
  of 
  Maple- 
  

   ton 
  village 
  has 
  the 
  most 
  glassy 
  groundmass 
  of 
  all 
  the 
  andesites, 
  

   and 
  its 
  devitrified 
  areas 
  have 
  the 
  micropoikilitic 
  structure 
  the 
  

   best 
  developed. 
  Two 
  outcrops 
  show 
  a 
  type 
  much 
  lighter 
  in 
  

   color 
  with 
  much 
  secondary 
  and 
  some 
  original 
  quartz, 
  giving 
  

   the 
  rock 
  a 
  dacite 
  facies. 
  The 
  other 
  sections 
  examined 
  are 
  of 
  

   the 
  typical 
  augite-andesite 
  or 
  hornblende-andesite 
  of 
  this 
  region, 
  

   and 
  require 
  no 
  detailed 
  description. 
  

  

  Andesites 
  of 
  Castle 
  Hill 
  — 
  JIacroscojnc 
  description. 
  — 
  The 
  

   rocks 
  at 
  this 
  place 
  do 
  not 
  have 
  the 
  character 
  of 
  lavas 
  which 
  

   have 
  formed 
  thick 
  flows, 
  but 
  suggest 
  rather 
  the 
  surface 
  of 
  a 
  

   flow 
  and 
  are 
  commonly 
  amygdaloidal, 
  or 
  even 
  slightly 
  brec- 
  

   ciated 
  and 
  ashy, 
  and 
  associated 
  with 
  them 
  is 
  an 
  abundance 
  of 
  

   true 
  volcanic 
  ash 
  with 
  lapilli. 
  The 
  rock 
  exposed 
  at 
  the 
  south- 
  

   east 
  base 
  of 
  the 
  hill 
  is 
  striking 
  in 
  its 
  field 
  appearance. 
  Black, 
  

   rusty-looking, 
  spheroidal 
  or 
  elliptical 
  masses 
  of 
  lava, 
  one 
  to 
  

   two 
  feet 
  in 
  diameter, 
  first 
  attract 
  the 
  attention 
  as 
  they 
  lie 
  

   loosely 
  strewn 
  over 
  the 
  surface. 
  The 
  solid 
  ledge 
  itself 
  is 
  seen 
  

   to 
  be 
  composed 
  of 
  these 
  forms, 
  which 
  have 
  their 
  outlines 
  well 
  

   displayed 
  by 
  weathering. 
  These 
  sack 
  like 
  or 
  pillow-shaped 
  

   masses 
  are 
  plainly 
  amygdaloidal 
  on 
  the 
  surface, 
  but 
  usually 
  

   much 
  denser 
  in 
  the 
  interior 
  and 
  are 
  cemented 
  together 
  by 
  a 
  

   coarse 
  breccia 
  of 
  rough 
  tabular, 
  spheroidal, 
  or 
  irregular 
  jagged 
  

   fragments 
  of 
  glassy 
  material 
  and 
  igneous 
  rock 
  of 
  similar 
  

   composition 
  to 
  the 
  spheres. 
  In 
  some 
  places, 
  noticeably 
  on 
  

   McDonald's 
  hill 
  to 
  the 
  south 
  of 
  Castle 
  Hill 
  proper, 
  this 
  struc- 
  

   ture 
  assumes 
  the 
  form 
  of 
  a 
  conglomerate 
  of 
  small 
  amygdaloidal 
  

   spheres 
  six 
  inches 
  and 
  less 
  in 
  diameter, 
  closely 
  cemented 
  

   together 
  with 
  angular 
  pebbles 
  of 
  andesite 
  and 
  other 
  igneous 
  

  

  Am. 
  Jour. 
  Sci. 
  — 
  Fourth 
  Series, 
  Vol. 
  VIII, 
  Xo. 
  47. 
  — 
  Xoyember, 
  1899. 
  

   25 
  

  

  