﻿M. 
  H. 
  Williams 
  — 
  Southern 
  Ice 
  Limit 
  in 
  Pennsylvania. 
  181 
  

  

  tion 
  are 
  also 
  seen 
  in 
  the 
  distribution 
  of 
  the 
  white 
  Medina 
  

   sandstone 
  of 
  Shamokin 
  Mountain 
  over 
  the 
  Salina 
  valley 
  to 
  the 
  

   southwest. 
  Farther 
  north 
  along 
  Penn's 
  creek 
  an 
  abundance 
  

   of 
  modified 
  drift 
  is 
  seen 
  capping 
  till 
  of 
  quicksands 
  and 
  

   bowlders 
  that 
  lie 
  against 
  the 
  glaciated 
  country 
  rock, 
  and 
  all 
  is 
  

   covered 
  with 
  slack 
  water 
  clays 
  from 
  the 
  Shade 
  Mountain 
  ice 
  

   dam, 
  or 
  the 
  one 
  formed 
  before 
  the 
  ice 
  abandoned 
  the 
  northern 
  

   end 
  of 
  Jack's 
  Mountain. 
  

  

  Action 
  of 
  the 
  ridges 
  on 
  the 
  ice 
  advance. 
  

  

  A 
  glance 
  at 
  the 
  map 
  shows 
  the 
  numerous 
  ridges 
  crossing 
  the 
  

   path 
  of 
  the 
  glacier. 
  These 
  rise 
  sharply 
  from 
  the 
  surrounding 
  

   country 
  to 
  600-1000 
  feet. 
  The 
  retention 
  of 
  a 
  large 
  mass 
  of 
  

   rotten 
  gneiss 
  on 
  the 
  northern 
  slope 
  of 
  the 
  South 
  Mountain 
  

   back 
  of 
  South 
  Bethlehem, 
  and 
  where 
  it 
  was 
  fully 
  exposed 
  to 
  

   the 
  force 
  of 
  the 
  ice 
  seemed 
  to 
  point 
  to 
  a 
  massing 
  of 
  the 
  ice 
  in 
  

   the 
  valley, 
  where 
  it 
  remained 
  stagnant, 
  while 
  a 
  shear 
  took 
  

   place 
  and 
  the 
  upper 
  part 
  of 
  the 
  ice 
  only 
  crossed 
  the 
  mountain. 
  

   This 
  is 
  also 
  shown 
  by 
  the 
  small 
  proportion 
  of 
  river 
  gravels 
  in 
  

   the 
  till 
  — 
  though 
  the 
  glacier 
  had 
  just 
  crossed 
  the 
  Lehigh. 
  

  

  In 
  "Report 
  G7 
  of 
  the 
  late 
  Pennsylvania 
  survey, 
  I. 
  C. 
  White 
  

   describes 
  the 
  glacial 
  deposits 
  in 
  the 
  tier 
  of 
  counties 
  along 
  the 
  

   north 
  branch 
  of 
  the 
  Susquehanna. 
  As 
  far 
  as 
  the 
  knowledge 
  

   of 
  the 
  subject 
  went 
  at 
  that 
  date, 
  the 
  report 
  is 
  accurate. 
  One 
  

   point 
  is 
  interesting 
  in 
  its 
  bearing 
  on 
  glacial 
  motion. 
  In 
  

   describing 
  the 
  gravels 
  in 
  Mifflin 
  township 
  he 
  notes 
  their 
  occur- 
  

   rence 
  only 
  at 
  comparatively 
  low 
  elevations 
  above 
  the 
  river. 
  

   The 
  writer 
  found 
  this 
  to 
  be 
  the 
  case, 
  and 
  made 
  a 
  trip 
  over 
  

   Nescopeck 
  Mountain 
  while 
  studying 
  the 
  matter. 
  It 
  seemed 
  

   strange 
  that 
  the 
  narrow 
  strip 
  of 
  land 
  lying 
  between 
  the 
  Susque- 
  

   hanna 
  and 
  the 
  mountain 
  should 
  be 
  free 
  from 
  gravels, 
  while 
  to 
  

   the 
  west 
  they 
  were 
  found 
  distributed 
  regularly 
  over 
  the 
  country 
  

   for 
  many 
  miles 
  south 
  of 
  the 
  river 
  and 
  in 
  some 
  cases 
  500 
  feet 
  

   above 
  it. 
  The 
  map 
  shows 
  that 
  Nescopeck 
  Mountain 
  rises 
  1000 
  

   feet 
  above 
  the 
  river 
  and 
  runs 
  parallel 
  to 
  it 
  for 
  some 
  miles 
  and, 
  

   at 
  Catawissa 
  (as 
  Catawissa 
  Mountain) 
  turns 
  southward 
  in 
  a 
  

   series 
  of 
  folds, 
  and 
  finally 
  resumes 
  its 
  former 
  trend, 
  as 
  Little 
  

   Mountain, 
  and 
  reaches 
  the 
  Susquehanna. 
  At 
  first 
  it 
  was 
  

   thought 
  that 
  the 
  mountain 
  turned 
  the 
  glacier 
  wholly 
  from 
  its 
  

   path 
  and 
  forced 
  it 
  to 
  scrape 
  along 
  its 
  northern 
  flank 
  till 
  its 
  

   bend 
  at 
  Catawissa 
  withdrew 
  the^resistance, 
  when 
  the 
  released 
  

   ice 
  resumed 
  its 
  former 
  line 
  of 
  motion 
  ; 
  but 
  the 
  finding 
  of 
  till 
  

   on 
  the 
  summit 
  of 
  the 
  mountain, 
  and 
  also 
  erratics 
  from 
  its 
  sum- 
  

   mit 
  that 
  were 
  carried 
  across 
  Scotch 
  valley 
  and 
  over 
  McCauleys 
  

   Mountain, 
  showed 
  that 
  the 
  ice 
  crossed 
  it. 
  Had 
  this 
  been 
  done 
  

   in 
  the 
  general 
  line 
  of 
  motion, 
  the 
  abundant 
  river 
  gravels 
  would 
  

  

  