﻿242 
  Lahee 
  — 
  New 
  Fossiliferous 
  Horizon 
  and 
  Underlying 
  

  

  sedimentary 
  series 
  which 
  forms 
  the 
  fold 
  appears 
  in 
  the 
  region 
  

   above 
  described, 
  where 
  the 
  lower 
  strata 
  rest 
  unconformably 
  on 
  

   the 
  Fitch 
  Hill 
  granite 
  gneiss. 
  It 
  is 
  interesting 
  to 
  notice 
  that 
  

   Hitchcock 
  mentions 
  an 
  unconformity 
  on 
  the 
  southeastern 
  side 
  

   of 
  the 
  syncline 
  about 
  seven 
  miles 
  southwest 
  of 
  Fitch 
  Hill, 
  

   northwest 
  of 
  the 
  town 
  of 
  Lisbon, 
  where 
  the 
  Blueberry 
  Mt. 
  

   argillites 
  meet 
  the 
  Swift 
  Water 
  series, 
  a 
  formation 
  supposed 
  

   to 
  be 
  equivalent 
  to 
  the 
  Lyman 
  schists 
  and 
  associated 
  rocks 
  on 
  

   the 
  northwest 
  side 
  of 
  the 
  syncline.* 
  

  

  In 
  passing 
  southward 
  from 
  the 
  Fitch 
  Hill 
  granite 
  gneiss, 
  

   crossing 
  the 
  strikes 
  of 
  the 
  strata, 
  one 
  encounters 
  in 
  succession 
  

   (going 
  upward, 
  stratigraphically) 
  (1) 
  the 
  basal 
  arkose 
  already 
  

   mentioned, 
  which 
  may 
  grade 
  locally 
  into 
  quartzite 
  beds 
  (2-80 
  

   feet 
  thick); 
  (2) 
  limestone 
  carrying 
  fossils 
  of 
  Niagaran 
  age 
  

   (30-40 
  feet) 
  ;f 
  (3) 
  calcareous 
  slate, 
  also 
  with 
  fossils 
  of 
  Niagaran 
  

   age 
  (6-10 
  feet 
  ; 
  (4) 
  non-fossiliferous 
  limestone 
  and 
  slate 
  (150 
  

   feet)* 
  ; 
  (5) 
  basic 
  sill 
  (thickness 
  uncertain 
  ; 
  not 
  great) 
  ; 
  (6) 
  thick 
  

   mass 
  of 
  arkose 
  forming 
  Fitch 
  Hill 
  and 
  therefore 
  called 
  the 
  

   Fitch 
  Hill 
  arkose 
  to 
  distinguish 
  it 
  from 
  the 
  basal 
  arkose 
  (200- 
  

   300 
  feet) 
  ; 
  (7) 
  basic 
  sill 
  (200 
  feet) 
  ; 
  (8) 
  banded 
  argillites 
  (450- 
  

   500 
  feet); 
  (9) 
  dark 
  gray 
  sandstone 
  with 
  dark 
  shale 
  layers 
  (to 
  

   the 
  crest 
  of 
  Blueberry 
  Mt.)4 
  The 
  first 
  four 
  and 
  the 
  sixth 
  

   members 
  we 
  have 
  called 
  the 
  ; 
  basal 
  series.' 
  Our 
  measurements 
  

   for 
  the 
  thickness 
  of 
  the 
  basal 
  series, 
  exclusive 
  of 
  the 
  sixth 
  

   member, 
  amounted 
  to 
  between 
  150 
  and 
  250 
  feet. 
  

  

  Further 
  proof 
  of 
  the 
  unconformity 
  beneath 
  these 
  sediments 
  

   is 
  presented 
  in 
  the 
  character 
  of 
  the 
  basal 
  arkose. 
  This 
  is 
  a 
  

   hard, 
  compact, 
  gritty 
  rock, 
  usually 
  without 
  the 
  least 
  indication 
  

   of 
  stratification. 
  In 
  one 
  or 
  two 
  outcrops, 
  however, 
  a 
  faint 
  

   streaky 
  appearance, 
  striking 
  and 
  dipping 
  parallel 
  to 
  the 
  strata 
  

   on 
  the 
  south, 
  suggests 
  that 
  there 
  was 
  a 
  very 
  slight 
  tendency 
  

   toward 
  sorting 
  of 
  the 
  disintegration 
  products 
  of 
  the 
  granite 
  

   gneiss 
  in 
  the 
  encroaching 
  Niagaran 
  sea. 
  The 
  feldspar 
  grains, 
  

   ranging 
  in 
  size 
  up 
  to 
  3/16" 
  or 
  1/4" 
  in 
  the 
  longest 
  dimension, 
  

   are 
  so 
  conspicuous 
  on 
  account 
  of 
  their 
  white 
  color 
  that 
  they 
  

   often 
  give 
  the 
  arkose 
  a 
  porphyritic 
  look. 
  They 
  are 
  of 
  the 
  

   same 
  kind 
  as 
  the 
  feldspars 
  in 
  the 
  Fitch 
  Hill 
  granite 
  gneiss 
  

   (orthoclase, 
  microperthite, 
  plagioclase, 
  and 
  some 
  microcline). 
  

   The 
  quartz, 
  together 
  with 
  a 
  very 
  little 
  chlorite, 
  constitutes 
  a 
  

   dark 
  background 
  for 
  the 
  feldspar. 
  In 
  thin 
  sections 
  the 
  quartz 
  

   is 
  seen 
  to 
  be 
  cracked 
  and 
  strained. 
  Secondary 
  calcite 
  occurs 
  

   as 
  veinlets 
  and 
  fillings 
  between 
  the 
  other 
  minerals. 
  

  

  As 
  a 
  rule 
  the 
  feldspar 
  in 
  the 
  basal 
  arkose 
  is 
  nearly 
  as 
  abun- 
  

   dant 
  as 
  the 
  quartz 
  ; 
  but 
  in 
  a 
  few 
  places 
  the 
  latter 
  becomes 
  rela- 
  

  

  * 
  Hitchcock 
  : 
  New 
  Studies 
  in 
  the 
  Ammonoosuc 
  District, 
  p. 
  478, 
  and 
  fig. 
  8 
  

   on 
  plate 
  42. 
  

  

  f 
  Hitchcock's 
  figures. 
  

  

  % 
  Called 
  ' 
  dark 
  gray 
  schists 
  ' 
  on 
  the 
  map. 
  

  

  