﻿174 
  E. 
  II 
  Williams 
  — 
  Southern 
  Ice 
  limit 
  in 
  Pennsylvania. 
  

  

  As 
  seen 
  from 
  the 
  western 
  slopes 
  of 
  the 
  White 
  Mountain 
  

   range, 
  the 
  next 
  range 
  to 
  the 
  eastward, 
  Silver 
  Peak, 
  is 
  appar- 
  

   ently 
  a 
  monocline 
  facing 
  westward 
  ; 
  but 
  from 
  the 
  known 
  struc- 
  

   ture 
  of 
  the 
  Great 
  Basin 
  ranges, 
  such 
  as 
  those 
  of 
  the 
  Eureka 
  

   district, 
  Nevada, 
  the 
  Oquirr 
  range, 
  Utah, 
  and 
  others 
  illustrated 
  

   by 
  the 
  geologists 
  of 
  the 
  Wheeler 
  Survey, 
  it 
  appears 
  that 
  in 
  the 
  

   broad 
  Paleozoic 
  area 
  between 
  the 
  Sierra 
  Nevada 
  on 
  the 
  west 
  

   and 
  the 
  early 
  Paleozoic 
  shoreline 
  on 
  the 
  east 
  (Colorado) 
  a 
  

   period 
  of 
  folding 
  and 
  thrust 
  faulting 
  was 
  followed 
  by 
  a 
  period 
  

   of 
  vertical 
  faulting, 
  which 
  displaced 
  the 
  strata 
  that 
  had 
  been 
  

   folded 
  and 
  faulted 
  in 
  the 
  preceding 
  epoch. 
  The 
  extent 
  and 
  

   character 
  of 
  this 
  disturbance 
  can 
  be 
  determined 
  only 
  by 
  a 
  care- 
  

   ful 
  study 
  of 
  each 
  of 
  the 
  mountain 
  ranges 
  for 
  a 
  distance 
  of 
  over 
  

   live 
  hundred 
  miles 
  east 
  and 
  west 
  and 
  probably 
  a 
  thousand 
  

   miles 
  north 
  and 
  south 
  ; 
  and 
  the 
  great 
  geologic 
  problems 
  will 
  

   not 
  be 
  fully 
  solved 
  until 
  the 
  areal 
  geology 
  of 
  the 
  region 
  

   between 
  the 
  109th 
  and 
  119th 
  meridians 
  shall 
  have 
  been 
  

   mapped. 
  

  

  Art. 
  XYII. 
  — 
  Notes 
  on 
  the 
  Southern 
  lee 
  Limit 
  in 
  Eastern 
  

   Pennsylvania 
  ; 
  by 
  Edward 
  H. 
  Williams. 
  

  

  The 
  accompanying 
  map 
  shows 
  what 
  has 
  been 
  done 
  during 
  

   the 
  past 
  year, 
  and 
  the 
  boundary 
  has 
  been 
  extended 
  from 
  the 
  

   Schuylkill 
  to 
  Lock 
  Haven. 
  There 
  probably 
  does 
  not 
  occur 
  as 
  

   diversified 
  a 
  field, 
  and 
  one 
  more 
  fortunately 
  situated, 
  than 
  that 
  

   which 
  stretches 
  from 
  the 
  Delaware 
  river 
  to 
  the 
  Alleghany 
  

   Mountain 
  in 
  Pennsylvania. 
  The 
  measures 
  from 
  the 
  Archaean 
  

   to 
  the 
  Trias 
  lie 
  under 
  all 
  states 
  of 
  deformation 
  and 
  weathering 
  

   and, 
  forming 
  all 
  arrangements 
  of 
  mountain 
  and 
  valley, 
  opposed 
  

   all 
  angles 
  of 
  trend 
  and 
  slope 
  to 
  the 
  approach 
  of 
  the 
  glacier. 
  

   The 
  lithological 
  and 
  fossiliferous 
  characters 
  of 
  those 
  measures 
  

   are 
  frequently 
  so 
  well 
  marked 
  that 
  their 
  fragments 
  can 
  be 
  

   quite 
  readily 
  recognized 
  under 
  all 
  conditions 
  of 
  weathering. 
  

   The 
  streams 
  of 
  the 
  region 
  run 
  toward 
  all 
  points 
  of 
  the 
  com- 
  

   pass, 
  and 
  the 
  Delaware, 
  Lehigh, 
  Schuylkill, 
  and 
  Susquehanna 
  

   are 
  of 
  constantly 
  large 
  volume, 
  and 
  flow 
  through 
  gaps 
  of 
  great 
  

   age 
  as 
  shown 
  by 
  their 
  low 
  angles, 
  and 
  over 
  preglacial 
  bottoms. 
  

   The 
  peculiar 
  systems 
  of 
  parallel 
  ridges 
  and 
  valleys 
  of 
  the 
  

   region 
  bring 
  great 
  differences 
  in 
  barometric 
  level 
  within 
  small 
  

   areas 
  ; 
  so 
  that 
  the 
  resistance 
  to 
  advance 
  of 
  the 
  ice 
  varied 
  

   greatly 
  within 
  short 
  distances 
  and, 
  at 
  times, 
  created 
  a 
  shear 
  in 
  

   the 
  interior 
  of 
  the 
  glacier. 
  The 
  varied 
  river 
  systems 
  also 
  dis- 
  

   tributed 
  the 
  glacial 
  trash 
  where 
  it 
  could 
  be 
  again 
  taken 
  up 
  by 
  

  

  