﻿of 
  the 
  Northern 
  Appalachians. 
  243 
  

  

  For 
  the 
  present 
  problem 
  the 
  topographic 
  maps 
  on 
  a 
  

   scale 
  of 
  1 
  : 
  62,500 
  are 
  of 
  a 
  suitable 
  horizontal 
  scale. 
  

   After 
  a 
  number 
  of 
  trials 
  the 
  vertical 
  scale 
  chosen 
  was 
  

   one 
  inch 
  equal 
  to 
  two 
  hundred 
  feet, 
  or 
  1: 
  2,400. 
  This 
  

   scale 
  is 
  convenient, 
  also, 
  because 
  it 
  permits 
  the 
  use 
  of 
  

   cross-section 
  paper 
  ruled 
  to 
  tenths 
  of 
  an 
  inch 
  ; 
  each 
  divi- 
  

   sion 
  thus 
  equals 
  20 
  feet, 
  which 
  is 
  the 
  usual 
  contour 
  inter- 
  

   val 
  of 
  the 
  topographic 
  maps 
  of 
  the 
  eastern 
  United 
  States. 
  

   This 
  vertical 
  scale, 
  twenty-six 
  times 
  the 
  horizontal, 
  

   grossly 
  exaggerates 
  the 
  relief 
  ; 
  it 
  is 
  necessary, 
  however, 
  

   in 
  order 
  to 
  clearly 
  distinguish 
  the 
  erosion 
  planes 
  on 
  the 
  

   Piedmont 
  slope 
  which 
  differ 
  in 
  elevation 
  only 
  by 
  one 
  to 
  

   two 
  hundred 
  feet. 
  

  

  The 
  writer 
  has 
  found 
  this 
  method 
  of 
  projected 
  profiles 
  

   of 
  so 
  much 
  use 
  in 
  the 
  present 
  study 
  that 
  a 
  detailed 
  illus- 
  

   tration 
  of 
  the 
  method 
  will 
  be 
  given, 
  both 
  for 
  the 
  purpose 
  

   of 
  showing 
  the 
  basis 
  on 
  which 
  the 
  projected 
  profiles 
  have 
  

   been 
  made 
  and 
  to 
  illustrate 
  the 
  adaptability 
  of 
  the 
  

   method 
  for 
  similar 
  problems. 
  

  

  The 
  method 
  is 
  essentially 
  as 
  follows. 
  A 
  strip 
  of 
  cross- 
  

   section 
  paper 
  is 
  fastened 
  parallel 
  to 
  the 
  lower 
  edge 
  of 
  

   the 
  drawing 
  board 
  and 
  the 
  topographic 
  sheet 
  is 
  fastened 
  

   above 
  so 
  that 
  the 
  direction 
  of 
  view 
  is 
  at 
  right-angles 
  to 
  

   the 
  length 
  of 
  the 
  section 
  and 
  thus 
  parallel 
  to 
  a 
  T-square 
  

   placed 
  against 
  the 
  lower 
  edge 
  of 
  the 
  drawing 
  board. 
  

   The 
  area 
  to 
  be 
  projected 
  is 
  outlined 
  on 
  the 
  map 
  and 
  the 
  

   contours 
  which 
  cut 
  the 
  front 
  edge 
  of 
  the 
  block 
  are 
  pro- 
  

   jected 
  first 
  to 
  give 
  the 
  foreground. 
  Then 
  the 
  topog- 
  

   raphy, 
  beginning 
  at 
  the 
  front 
  and 
  working 
  toward 
  the 
  

   back 
  of 
  the 
  block, 
  is 
  systematically 
  projected 
  onto 
  the 
  

   cross-section 
  paper 
  with 
  the 
  aid 
  of 
  the 
  T-square. 
  As 
  

   each 
  hill 
  is 
  outlined 
  on 
  the 
  section 
  a 
  line 
  is 
  drawn 
  through 
  

   it 
  on 
  the 
  map 
  to 
  show 
  that 
  it 
  has 
  been 
  projected 
  and 
  this 
  

   also 
  gives 
  a 
  record 
  of 
  the 
  progress 
  of 
  the 
  work. 
  Each 
  

   successive 
  belt 
  of 
  topography 
  shuts 
  out 
  all 
  behind 
  it 
  ex- 
  

   cept 
  the 
  higher 
  elevations, 
  thus 
  indicating 
  what 
  features 
  

   are 
  to 
  be 
  projected 
  as 
  the 
  work 
  progresses. 
  At 
  the 
  out- 
  

   set 
  it 
  is 
  advisable 
  to 
  study 
  the 
  topography 
  of 
  a 
  region 
  

   first 
  from 
  the 
  map 
  in 
  order 
  to 
  become 
  thoroughly 
  famil- 
  

   iar 
  with 
  it. 
  When, 
  however, 
  this 
  familiarity 
  has 
  been 
  

   gained, 
  as 
  well 
  as 
  experience 
  in 
  the 
  method 
  of 
  projection, 
  

   profiles 
  of 
  this 
  character 
  can 
  be 
  built 
  up 
  quite 
  rapidly 
  

   and 
  with 
  little 
  mental 
  labor. 
  

  

  [It 
  should 
  be 
  said 
  in 
  regard 
  to 
  projected 
  profiles 
  that 
  

   they 
  are 
  objective 
  with 
  respect 
  to 
  summit 
  elevations 
  but 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XLIX, 
  No. 
  292.— 
  April, 
  1920. 
  

   18 
  

  

  