﻿184 
  E. 
  H. 
  Williams 
  — 
  Southern 
  Ice 
  Limit 
  in 
  Pennsylvania. 
  

  

  ward 
  to 
  the 
  valley 
  of 
  Perm's 
  creek 
  the 
  surface 
  was 
  clear, 
  but 
  

   the 
  glacial 
  flow 
  through 
  that 
  creek 
  was 
  seen 
  to 
  have 
  come 
  from 
  

   Brush 
  valley. 
  

  

  At 
  Mill 
  Hall 
  twelve 
  feet 
  of 
  slack 
  water 
  deposits 
  overlie 
  what 
  

   seems 
  to 
  be 
  sub-glacial 
  till, 
  and 
  the 
  Bald 
  Eagle 
  valley 
  soon 
  

   becomes 
  perfectly 
  flat 
  and 
  filled 
  with 
  debris, 
  from 
  which 
  the 
  

   small 
  knolls 
  formed 
  by 
  varying 
  outcrops 
  appeared 
  in 
  a 
  sub- 
  

   merged 
  state. 
  These 
  deposits 
  were 
  followed 
  continuously 
  

   over 
  the 
  divide 
  at 
  1110 
  A. 
  T., 
  or 
  600 
  feet 
  above 
  the 
  river 
  at 
  

   Williamsport, 
  and 
  down 
  the 
  Juniata 
  to 
  Huntingdon. 
  Where- 
  

   ever 
  they 
  exist 
  at 
  great 
  depths 
  in 
  the 
  latter 
  valley 
  there 
  is 
  evi- 
  

   dence 
  of 
  slack 
  water, 
  as 
  below 
  them 
  there 
  is 
  a 
  contraction 
  of 
  

   the 
  channel, 
  where 
  it 
  passes 
  through 
  the 
  gaps 
  in 
  the 
  numerous 
  

   ridges. 
  When 
  we 
  consider 
  that 
  the 
  whole 
  discharge 
  from 
  the 
  

   central 
  part 
  of 
  the 
  state 
  glacier 
  passed 
  through 
  Bald 
  Eagle 
  and 
  

   Juniata 
  valleys, 
  we 
  can 
  see 
  at 
  once 
  that 
  small 
  ice 
  dams 
  must 
  

   have 
  been 
  continually 
  forming 
  in 
  these 
  narrow 
  gorges, 
  from 
  the 
  

   floating 
  bergs, 
  and 
  as 
  these 
  deposits 
  are 
  found 
  from 
  the 
  present 
  

   level 
  of 
  the 
  river 
  to 
  an 
  average 
  of 
  80 
  feet 
  above 
  it, 
  we 
  can 
  get 
  

   an 
  idea 
  of 
  the 
  depth 
  of 
  the 
  water. 
  In 
  one 
  case, 
  a 
  dam 
  sent 
  

   cakes 
  of 
  ice 
  from 
  300-400 
  feet 
  up 
  the 
  slope 
  of 
  Warrior 
  Ridge 
  

   to 
  make 
  a 
  small 
  deposit 
  of 
  erratics. 
  That 
  the 
  discharge 
  was 
  

   torrential 
  is 
  seen 
  by 
  the 
  erosion 
  of 
  the 
  rotten 
  limestone 
  at 
  Bar- 
  

   ree 
  on 
  the 
  up-stream 
  side 
  of 
  the 
  ridge, 
  and 
  its 
  retention 
  on 
  the 
  

   other 
  side 
  to 
  great 
  depths. 
  We 
  can 
  imagine, 
  therefore, 
  during 
  

   a 
  portion 
  of 
  the 
  earliest 
  part 
  of 
  glacial 
  times, 
  a 
  deep 
  lake 
  

   extending 
  from 
  Williamsport 
  above 
  the 
  junction 
  of 
  the 
  Sus- 
  

   quehanna 
  and 
  Sinnemahoning; 
  filling 
  Nippenose, 
  upper 
  dit- 
  

   tany 
  and 
  Bald 
  Eagle 
  valleys, 
  and 
  discharging 
  a 
  deep 
  torrent 
  

   through 
  the 
  Juniata. 
  A 
  smaller 
  side 
  discharge 
  from 
  the 
  same 
  

   glacier 
  went 
  down 
  Penn's 
  creek 
  to 
  the 
  Susquehanna 
  ; 
  but 
  was 
  

   stopped 
  by 
  the 
  ice 
  at 
  Shade 
  Mt. 
  for 
  a 
  time 
  and 
  sent 
  down 
  to 
  

   Lewistown, 
  on 
  the 
  Juniata 
  ; 
  but 
  afterwards 
  was 
  freed 
  and 
  

   allowed 
  to 
  reach 
  the 
  Susquehanna 
  at 
  Selin's 
  Grove. 
  This 
  great 
  

   glacial 
  lake 
  has 
  been 
  called 
  by 
  the 
  writer, 
  in 
  honor 
  of 
  our 
  

   State 
  geologist, 
  Lake 
  Lesley. 
  

  

  Detailed 
  sections 
  were 
  photographed 
  at 
  various 
  places 
  

   through 
  the 
  Bald 
  Eagle 
  and 
  Juniata 
  valleys. 
  At 
  the 
  northern 
  

   entrance 
  of 
  the 
  former, 
  at 
  Mill 
  Hall, 
  there 
  is 
  a 
  considerable 
  

   flood 
  cone 
  attached 
  to 
  the 
  southern 
  side 
  of 
  the 
  gap 
  in 
  Bald 
  

   Eagle 
  Mt., 
  where 
  the 
  flow 
  was 
  turned 
  south 
  from 
  the 
  dittany 
  

   valley. 
  Along 
  the 
  Central 
  railroad 
  of 
  Penn., 
  through 
  the 
  

   latter 
  valley, 
  there 
  exist 
  thick 
  deposits 
  of 
  glacial 
  drift 
  distribu- 
  

   ted 
  from 
  the 
  gaps 
  to 
  the 
  east, 
  and 
  the 
  larger 
  material 
  lies 
  

   close 
  against 
  the 
  Sittany 
  Mt. 
  on 
  the 
  eastern 
  side 
  of 
  the 
  valley, 
  

   while 
  the 
  fine 
  clays 
  extend 
  over 
  the 
  whole 
  valley. 
  The 
  flood 
  

   cone 
  at 
  Mill 
  Hall, 
  therefore, 
  does 
  not 
  contain 
  gravel 
  in 
  its 
  

  

  