﻿Related 
  Sedimentary 
  Surface 
  Forms. 
  199 
  

  

  All 
  of 
  these 
  factors 
  seem 
  to 
  approach 
  a 
  minimum 
  in 
  

   desert 
  regions 
  with 
  winds 
  of 
  constant 
  direction 
  and 
  

   unlimited 
  sand 
  supply. 
  Turning 
  to 
  such 
  regions, 
  we 
  find 
  

   there 
  two 
  radically 
  different 
  types 
  of 
  dunes 
  : 
  transverse 
  

   and 
  longitudinal 
  dunes. 
  The 
  former 
  were 
  perhaps 
  

   observed 
  on 
  the 
  largest 
  scale 
  by 
  Sven 
  Hedin 
  who 
  traveled 
  

   for 
  months 
  through 
  dune 
  regions 
  of 
  the 
  Takla-makan 
  

   desert 
  of 
  inner 
  Asia, 
  in 
  which 
  one 
  dune 
  crest 
  followed 
  the 
  

   other 
  at 
  uniform 
  intervals 
  of 
  several 
  kilometers, 
  each 
  

   about 
  150 
  m. 
  high. 
  62 
  

  

  Longitudinal 
  dunes 
  are 
  developed 
  on 
  a 
  large 
  scale 
  in 
  

   the 
  extensive 
  dune 
  area 
  separating 
  the 
  oases 
  Dakhleh 
  

   and 
  Kufra 
  in 
  the 
  Libyan 
  desert, 
  where 
  the 
  north-north- 
  

  

  Fig. 
  9. 
  

   A 
  

  

  • 
  1 
  <5lTl. 
  

  

  Fig. 
  9. 
  Diagrams 
  to 
  contrast 
  current 
  -ripples 
  (A) 
  and 
  sand-waves 
  (B). 
  

   Sand 
  grains 
  in 
  motion 
  represented 
  by 
  dots; 
  the 
  sediment 
  at 
  rest 
  shown 
  in 
  

   black. 
  

  

  west 
  trend 
  of 
  these 
  dunes, 
  parallel 
  to 
  the 
  direction 
  of 
  the 
  

   prevailing 
  winds, 
  effectively 
  prevents 
  direct 
  communica- 
  

   tion 
  between 
  the 
  two 
  oases. 
  63 
  

  

  According 
  to 
  Cornish 
  (1897, 
  pp. 
  294-5), 
  both 
  types 
  

   occur 
  in 
  the 
  Indian 
  desert. 
  Near 
  the 
  Rann 
  of 
  Cutch, 
  the 
  

   dunes 
  are 
  longitudinal; 
  further 
  inland 
  they 
  are 
  trans- 
  

   verse, 
  and 
  between 
  the 
  two 
  districts 
  intermediate 
  forms 
  

   are 
  shown 
  on 
  the 
  maps. 
  Cornish 
  considers 
  the 
  strength 
  

   of 
  the 
  wind 
  as 
  the 
  most 
  important 
  factor 
  conditioning 
  the 
  

   difference 
  between 
  longitudinal 
  and 
  transverse 
  dunes. 
  

  

  VI. 
  General 
  Conclusions. 
  

  

  In 
  the 
  preceding 
  chapters 
  the 
  various 
  surface 
  forms 
  of 
  

   sediments 
  discussed 
  were 
  interpreted 
  as 
  offering 
  a 
  mini- 
  

  

  62 
  Quoted 
  from 
  Solger, 
  Duenenbuch, 
  p. 
  154. 
  

  

  ^Beadnell, 
  H. 
  J. 
  L., 
  Geogr. 
  Journal, 
  vol. 
  35, 
  p. 
  379 
  ff., 
  1910. 
  

  

  