﻿204: 
  F. 
  Lever 
  ett 
  — 
  Pleistocene 
  Fluvial 
  Planes 
  of 
  

  

  highest 
  of 
  the 
  beaches 
  in 
  the 
  eastern 
  part 
  of 
  the 
  expanded 
  

   Lake 
  Erie. 
  This 
  beach 
  is 
  fully 
  80 
  feet 
  higher 
  immediately 
  

   north 
  of 
  Chautauqua 
  lake 
  than 
  it 
  is 
  at 
  the 
  Grand 
  river 
  basin. 
  

   Since 
  this 
  amount 
  of 
  differential 
  uplift 
  has 
  occurred 
  during 
  

   the 
  short 
  time 
  since 
  the 
  lake 
  occupied 
  this 
  beach, 
  it 
  becomes 
  

   necessary 
  to 
  allow 
  for 
  even 
  greater 
  changes 
  either 
  of 
  depres- 
  

   sion 
  or 
  of 
  uplift 
  in 
  the 
  much 
  longer 
  period 
  that 
  has 
  elapsed 
  

   since 
  the 
  high-level 
  terraces 
  along 
  the 
  streams 
  of 
  western 
  

   Pennsylvania 
  were 
  formed. 
  

  

  On 
  the 
  whole, 
  therefore, 
  the 
  balance 
  of 
  evidence 
  favors 
  the 
  

   Shenango 
  as 
  against 
  the 
  Mahoning 
  route, 
  but 
  the 
  question 
  is 
  

   still 
  an 
  open 
  one. 
  The 
  definite 
  conclusions 
  of 
  Mr. 
  Foshay 
  

   supported 
  by 
  map 
  and 
  proposed 
  name 
  do 
  not 
  seem 
  to 
  be 
  war- 
  

   ranted 
  by 
  the 
  present 
  state 
  of 
  evidence, 
  or 
  even 
  to 
  represent 
  

   the 
  probabilities 
  of 
  the 
  case. 
  

  

  Interglacial 
  valleys 
  {Buried 
  channels). 
  — 
  As 
  the 
  high-level 
  

   base-plane 
  has 
  been 
  demonstrably 
  connected 
  with 
  the 
  earlier 
  

   glacial 
  epoch 
  by 
  Dr. 
  Chance 
  and 
  President 
  Chamberlin, 
  the 
  

   channels 
  cut 
  in 
  it 
  are 
  obviously 
  of 
  later 
  age 
  ; 
  and 
  it 
  is 
  impor- 
  

   tant 
  that 
  the 
  existing 
  broad 
  distinction 
  between 
  the 
  interglacial 
  

   and 
  preglacial 
  channels 
  of 
  this 
  region 
  be 
  kept 
  in 
  mind 
  ; 
  the 
  

   preglacial 
  channels 
  have, 
  so 
  far 
  as 
  yet 
  identified, 
  a 
  fluvial 
  plane 
  

   far 
  above 
  that 
  of 
  the 
  present 
  streams, 
  while 
  the 
  interglacial 
  

   channels 
  have 
  a 
  rock 
  floor 
  in 
  large 
  part 
  below 
  the 
  present 
  

   streams. 
  

  

  The 
  study 
  of 
  the 
  profiles 
  of 
  the 
  valley 
  floors 
  within 
  this 
  

   drift-covered 
  region, 
  when 
  combined 
  with 
  an 
  attempt 
  to 
  

   restore 
  former 
  systems 
  of 
  drainage, 
  is 
  calculated 
  to 
  impress 
  

   one 
  with 
  the 
  fragmentary 
  nature 
  of 
  available 
  evidence 
  It 
  is 
  

   true 
  that 
  portions 
  of 
  Big 
  Sandy, 
  Oil 
  and 
  French 
  creeks 
  and 
  of 
  

   the 
  Allegheny 
  and 
  Conewango 
  rivers 
  are 
  sufficiently 
  well 
  

   explored 
  by 
  the 
  numerous 
  oil-well 
  borings 
  to 
  give 
  a 
  satisfactory 
  

   knowledge 
  of 
  the 
  slope 
  of 
  the 
  valley 
  floors, 
  but 
  outside 
  of 
  the 
  

   oil 
  district 
  the 
  valleys 
  have 
  been 
  explored 
  only 
  so 
  far 
  as 
  is 
  

   necessary 
  to 
  obtain 
  water 
  or 
  to 
  prove 
  that 
  oil 
  and 
  gas 
  are 
  not 
  

   to 
  be 
  found. 
  Throughout 
  much 
  of 
  northwestern 
  Pennsyl- 
  

   vania 
  and 
  northeastern 
  Ohio 
  the 
  depth 
  of 
  drift 
  in 
  valleys 
  

   is 
  known 
  only 
  at 
  intervals 
  of 
  several 
  miles, 
  and 
  very 
  seldom 
  

   has 
  a 
  series 
  of 
  borings 
  been 
  made 
  that 
  test 
  the 
  entire 
  breadth 
  

   of 
  a 
  valley. 
  

  

  Mr. 
  Foshay 
  calls 
  attention 
  to 
  the 
  very 
  low 
  altitude 
  of 
  the 
  

   rock 
  floor 
  near 
  the 
  junction 
  of 
  the 
  Mahoning 
  and 
  Shenango 
  

   rivers, 
  where 
  it 
  is 
  said 
  to 
  be 
  50-75 
  feet 
  below 
  the 
  level 
  of 
  the 
  

   floor 
  of 
  the 
  Ohio 
  near 
  Pittsburg, 
  and 
  perhaps 
  lower 
  than 
  at 
  

   the 
  mouth 
  of 
  the 
  Beaver, 
  and 
  bases 
  his 
  u 
  Spencer 
  River" 
  

   channel 
  largely 
  upon 
  this 
  deep 
  portion 
  of 
  the 
  valley, 
  no 
  bor- 
  

   ings 
  having 
  yet 
  been 
  made 
  farther 
  up-stream 
  along 
  either 
  the 
  

  

  