﻿Report 
  of 
  the 
  State 
  Geologist. 
  661 
  

  

  Lewis. 
  

  

  Series 
  I. 
  The 
  only 
  exposure 
  of 
  undoubted 
  gneiss, 
  or 
  of 
  a 
  

   gneiss 
  consisting 
  of 
  microperthite 
  and 
  quartz, 
  is 
  the 
  peculiar 
  

   included 
  mass 
  shown 
  in 
  section 
  A 
  A. 
  It 
  is 
  enveloped 
  in 
  gabbro 
  

   and 
  the 
  component 
  minerals 
  are 
  so 
  shattered 
  that 
  it 
  seems 
  almost 
  

   elastic 
  and 
  might, 
  were 
  it 
  not 
  for 
  the 
  few 
  large 
  orthoclases 
  that 
  

   have 
  escaped. 
  It 
  is 
  one 
  of 
  the 
  best 
  examples 
  of 
  the 
  intrusive 
  

   nature 
  of 
  series 
  III. 
  The 
  roads 
  to 
  the 
  northwestern 
  corner 
  of 
  

   the 
  town 
  were 
  destroyed 
  by 
  the 
  freshet 
  so 
  that 
  we 
  could 
  not 
  cross 
  

   that 
  area, 
  but 
  shall 
  reach 
  it 
  from 
  the 
  neighboring 
  town 
  of 
  Jay, 
  

   which 
  remains 
  to 
  be 
  traversed. 
  There 
  are 
  many 
  gneissoid 
  rocks 
  

   in 
  Lewis, 
  but 
  they 
  all 
  showed, 
  under 
  the 
  microscope, 
  only 
  horn- 
  

   blende, 
  pyroxene 
  and 
  plagioclase 
  and 
  were, 
  therefore, 
  referred 
  to 
  

   series 
  III. 
  

  

  Series 
  II 
  The 
  central 
  area 
  colored 
  for 
  this 
  series 
  is 
  most 
  

   peculiar. 
  At 
  63 
  to 
  66 
  it 
  is 
  practically 
  a 
  great 
  ridge 
  of 
  nearly 
  pure 
  

   quartz. 
  The 
  mineral 
  shows 
  various 
  shades, 
  and 
  outcrops 
  for 
  2,300 
  

   paces 
  across 
  the 
  strike. 
  Some 
  little 
  feldspathic 
  gneiss 
  or 
  pegma- 
  

   tite 
  appears, 
  and 
  a 
  little 
  ophicalcite. 
  The 
  exposure 
  was 
  regarded 
  

   as 
  a 
  member 
  of 
  series 
  II, 
  which 
  had 
  suffered 
  from 
  excessive 
  meta- 
  

   morphism 
  by 
  contact 
  with 
  the 
  surrounding 
  norite. 
  Probably 
  from 
  

   this 
  area 
  the 
  wollastonite 
  was 
  derived, 
  which 
  is 
  recorded 
  by 
  the 
  

   early 
  reports. 
  Pegmatite 
  occurs 
  at 
  66a. 
  Hornblendic 
  gneiss 
  out- 
  

   crops 
  at 
  7?, 
  and 
  at 
  72 
  graphitic 
  quartzite 
  was 
  found, 
  though 
  not 
  

   certainly 
  in 
  place. 
  A 
  gabbro 
  intrusion 
  penetrates 
  at 
  69-70. 
  

  

  These 
  exposures 
  may 
  run 
  further 
  north. 
  The 
  broken 
  bridges 
  

   cut 
  us 
  off 
  from 
  exploring 
  it 
  as 
  thoroughly 
  as 
  we 
  wished. 
  The 
  

   northwestern 
  portion 
  is 
  very 
  wild, 
  with 
  hardly 
  a 
  house. 
  

  

  Series 
  III. 
  The 
  anorthosites 
  and 
  gabbros 
  cover 
  the 
  greater 
  

   part 
  of 
  Lewis. 
  Both 
  are 
  found 
  in 
  excellent 
  development. 
  In 
  

   the 
  southeastern 
  portion 
  varieties 
  occur 
  which 
  are 
  rich 
  in 
  biotite 
  

   (59, 
  59a), 
  and 
  in 
  No. 
  59 
  hypersthene 
  is 
  present 
  in 
  large 
  crystals. 
  

   In 
  the 
  gabbros 
  of 
  the 
  extreme 
  west 
  biotite 
  is 
  also 
  notable. 
  The 
  

   feldspars 
  contain 
  the 
  numerous 
  inclusions 
  which 
  are 
  character- 
  

   istic 
  of 
  the 
  gabbros. 
  They 
  are 
  regular 
  geometrical 
  shapes, 
  of 
  

   more 
  or 
  less 
  perfect 
  hexagonal 
  outline. 
  They 
  are 
  ranged 
  along 
  

   lines 
  that 
  intersect 
  at 
  sixty 
  degrees, 
  and 
  resemble 
  sagenite 
  nets 
  of 
  

   rutile. 
  The 
  needles 
  are 
  pleochroic 
  yellow 
  the 
  long 
  way, 
  and 
  

   colorless 
  the 
  short. 
  The 
  hexagonal 
  scales 
  are 
  probably 
  mica- 
  

   ceous 
  ilmenite, 
  and 
  the 
  rods 
  rutile. 
  

  

  