﻿Western 
  Pennsylvania. 
  20T 
  

  

  glacial 
  terraces 
  from 
  its 
  northern 
  tributaries 
  above 
  Wellsburg, 
  

   West 
  Virginia, 
  and 
  all 
  these 
  terraces 
  continue 
  down 
  the 
  Ohio 
  

   and 
  have 
  a 
  fall 
  as 
  great 
  as 
  the 
  present 
  stream, 
  showing 
  that 
  an 
  

   open 
  valley 
  existed 
  previous 
  to 
  the 
  later 
  glacial 
  period 
  and 
  

   that 
  its 
  stream 
  has 
  since 
  this 
  glacial 
  period 
  been 
  reexcavating 
  

   a 
  channel 
  partially 
  filled 
  by 
  glacial 
  gravels. 
  Furthermore, 
  gas 
  

   well 
  borings 
  at 
  Wellsburg, 
  West 
  Virginia, 
  where 
  Mr. 
  Foshay 
  

   lias 
  placed 
  the 
  old 
  watershed, 
  show 
  the 
  rock 
  floor 
  there 
  to 
  be 
  

   but 
  590 
  feet 
  A. 
  T. 
  or 
  10 
  feet 
  lower 
  than 
  it 
  is 
  known 
  to 
  be 
  at 
  

   any 
  point 
  along 
  the 
  Ohio 
  in 
  Pennsylvania. 
  A 
  carefully 
  pre- 
  

   pared 
  report 
  of 
  a 
  well 
  has 
  been 
  sent 
  me 
  by 
  Millard 
  E. 
  Boyd, 
  

   Esq., 
  city 
  engineer 
  of 
  Wellsburg, 
  in 
  which 
  the 
  character 
  and 
  

   thickness 
  of 
  drift 
  are 
  given 
  and 
  the 
  altitude 
  of 
  the 
  rock 
  floor 
  

   is 
  referred 
  to 
  low 
  water 
  in 
  the 
  Ohio, 
  from 
  which 
  it 
  appears 
  

   that 
  the 
  drift 
  below 
  the 
  level 
  of 
  low 
  water 
  mark 
  is 
  gravel, 
  

   showing 
  vigorous 
  drainage, 
  and 
  the 
  rock 
  floor 
  is 
  40*58 
  feet 
  

   below 
  low 
  water. 
  Mr. 
  Boyd 
  states 
  that 
  within 
  a 
  radius 
  of 
  two 
  

   miles 
  about 
  thirty 
  wells 
  have 
  been 
  made 
  and 
  that 
  those 
  on 
  the 
  

   same 
  bottom 
  with 
  the 
  one 
  reported 
  all 
  show 
  the 
  rock 
  floor 
  to 
  

   have 
  about 
  the 
  same 
  altitude 
  (590 
  feet 
  A. 
  T.) 
  

  

  This 
  evidence 
  from 
  the 
  Ohio 
  valley 
  seems 
  conclusive 
  that 
  

   the 
  Monongahela 
  and 
  Allegheny 
  rivers 
  had 
  their 
  present 
  course 
  

   down 
  the 
  Ohio 
  in 
  the 
  interglacial 
  period 
  and 
  have 
  held 
  it 
  con- 
  

   tinuously 
  from 
  that 
  time 
  to 
  the 
  present. 
  

  

  In 
  view 
  of 
  the 
  results 
  arrived 
  at 
  by 
  the 
  study 
  of 
  this 
  portion 
  

   of 
  the 
  Upper 
  Ohio 
  district, 
  we 
  are 
  naturally 
  led 
  to 
  examine 
  

   the 
  nature 
  of 
  the 
  evidence 
  put 
  forth 
  by 
  Mr. 
  J. 
  F. 
  Carll 
  some 
  

   years 
  ago,* 
  as 
  a 
  demonstration 
  that 
  the 
  buried 
  channels 
  of 
  the 
  

   upper 
  Allegheny, 
  Conewango, 
  Oil, 
  and 
  French 
  creeks 
  have 
  

   an 
  outlet 
  into 
  the 
  Lake 
  Erie 
  basin. 
  In 
  discussing 
  this 
  evidence 
  

   the 
  buried 
  channels 
  (interglacial 
  fluvial 
  planes) 
  only 
  are 
  con- 
  

   sidered 
  and 
  no 
  account 
  is 
  taken 
  of 
  the 
  high 
  terraces 
  (pregla- 
  

   cial 
  fluvial 
  planes) 
  since 
  these 
  high 
  planes 
  have 
  not 
  been 
  

   sufficiently 
  investigated 
  north 
  of 
  the 
  glacial 
  boundary 
  to 
  enable 
  

   one 
  to 
  form 
  an 
  opinion 
  concerning 
  them. 
  

  

  The 
  numerous 
  oil 
  well 
  borings 
  show 
  that 
  the 
  valley 
  floors 
  of 
  

   several 
  northern 
  tributaries 
  of 
  the 
  Allegheny 
  have 
  higher 
  

   altitudes 
  near 
  the 
  mouths 
  of 
  these 
  tributaries 
  than 
  they 
  have 
  a 
  

   few 
  miles 
  upstream. 
  For 
  example, 
  in 
  the 
  Conewango 
  valley 
  

   the 
  rock 
  floor 
  is 
  129 
  feet 
  lower 
  at 
  Fentonville, 
  near 
  the 
  State 
  

   line 
  of 
  New 
  York 
  and 
  Pennsylvania, 
  than 
  it 
  is 
  at 
  the 
  mouth 
  of 
  

   the 
  stream, 
  13 
  miles 
  south, 
  and 
  the 
  rock 
  floor 
  of 
  Little 
  Broken- 
  

   straw 
  valley 
  is 
  148 
  feet 
  lower 
  at 
  Lottsville, 
  Penn. 
  (No. 
  1), 
  

   than 
  where 
  its 
  waters 
  join 
  the 
  Allegheny 
  15 
  miles 
  below. 
  In 
  

   other 
  tributaries 
  of 
  the 
  Allegheny 
  the 
  descent 
  of 
  the 
  rock 
  floor 
  

   begins 
  a 
  few 
  miles 
  above 
  the 
  mouth 
  ; 
  thus 
  in 
  Oil 
  creek 
  the 
  

  

  * 
  Penn. 
  2d 
  Geol. 
  Survey 
  III, 
  1880, 
  pp. 
  330-366. 
  

  

  