﻿176 
  Bucher 
  — 
  Origin 
  of 
  Ripples, 
  and 
  

  

  only 
  to 
  a 
  superficial 
  layer 
  formed 
  just 
  before 
  exposure. 
  

   One 
  case 
  forms 
  an 
  exception. 
  "On 
  one 
  of 
  the 
  shoals 
  

   the 
  sand 
  is 
  mixed 
  with 
  stones 
  and 
  cockle-shells. 
  . 
  . 
  . 
  

   The 
  leeward 
  portions 
  . 
  . 
  . 
  consists 
  of 
  sand 
  which 
  has 
  

   been 
  picked 
  out 
  from 
  among 
  the 
  coarser 
  materials, 
  held 
  

   floating 
  for 
  a 
  time 
  in 
  "eddying 
  suspension, 
  " 
  and 
  finally 
  

   deposited 
  on 
  the 
  lee 
  of 
  the 
  ridge. 
  The 
  weather 
  side 
  of 
  

   the 
  ridges, 
  now 
  faced 
  with 
  shingle 
  and 
  cockle-shells, 
  

   assumes 
  a 
  slope 
  almost 
  as 
  steep 
  as 
  the 
  talus 
  of 
  the 
  lee- 
  

   side, 
  because 
  the 
  coarser 
  material 
  does 
  not 
  slide 
  so 
  

   readily 
  as 
  the 
  finer 
  sand 
  would 
  do 
  under 
  like 
  conditions. 
  27 
  

  

  3. 
  Traveling. 
  — 
  By 
  means 
  of 
  stakes 
  driven 
  to 
  a 
  depth 
  

   of 
  about 
  three 
  feet 
  into 
  the 
  sand, 
  in 
  Montrose 
  Harbor, 
  

   N. 
  B., 
  Cornish 
  studied 
  the 
  changes 
  of 
  a 
  series 
  of 
  sand- 
  

   waves 
  for 
  several 
  weeks 
  in 
  detail. 
  

  

  Toward 
  neap 
  tides 
  the 
  ridges 
  facing 
  with 
  the 
  ebb 
  were 
  

   smoothed 
  out 
  and 
  the 
  sands 
  remained 
  almost 
  featureless. 
  

   "As 
  the 
  tides 
  increase, 
  well-defined 
  steep 
  ridges 
  appear, 
  

   which 
  grow 
  in 
  height 
  and 
  also 
  apparently 
  by 
  elimination 
  

   of 
  certain 
  ridges, 
  in 
  average 
  wave-length. 
  As 
  the 
  tides 
  

   fall 
  off 
  again 
  the 
  height 
  or 
  amplitude 
  of 
  the 
  ridges 
  

   rapidly 
  decreases, 
  the 
  wave-length 
  decreasing 
  very 
  

   slowly' 
  ' 
  (p. 
  194), 
  In 
  three 
  days 
  the 
  amplitude 
  dimin- 
  

   ished 
  42 
  per 
  cent, 
  the 
  wave-length 
  only 
  2 
  per 
  cent, 
  that 
  

   is, 
  remained 
  practically 
  constant. 
  

  

  These 
  sand-waves 
  show 
  a 
  daily 
  advance 
  toward 
  the 
  lee, 
  

   which 
  in 
  the 
  case 
  mentioned 
  above 
  amounted 
  to 
  an 
  

   average 
  of 
  83 
  cm. 
  a 
  day. 
  This 
  advance 
  is, 
  of 
  course, 
  

   limited 
  to 
  the 
  relatively 
  short 
  duration 
  of 
  high 
  water 
  

   twice 
  a 
  day. 
  

  

  In 
  some 
  cases, 
  Cornish 
  observed 
  that 
  certain 
  sand- 
  

   waves 
  became 
  stationary, 
  while 
  others 
  near 
  by 
  moved 
  

   freely 
  with 
  the 
  tides, 
  the 
  former 
  differing 
  not 
  only 
  in 
  size, 
  

   but 
  also 
  in 
  tone 
  of 
  color 
  from 
  the 
  ordinary 
  ridges. 
  "On 
  

   the 
  whole 
  it 
  seems 
  that 
  among 
  the 
  tidal 
  sand-ridges, 
  

   which 
  are 
  exposed 
  at 
  low 
  water, 
  a 
  setting 
  of 
  the 
  sand 
  

   sometimes 
  occurs' 
  ' 
  (p. 
  194). 
  

  

  4. 
  For 
  data 
  concerning 
  wave-length 
  and 
  amplitude, 
  

   see 
  table 
  4. 
  

  

  3. 
  Formation 
  of 
  Sand-waves. 
  

  

  It 
  is 
  suggested 
  that 
  the 
  term 
  " 
  sand- 
  waves 
  ' 
  ' 
  be 
  defined 
  

   to 
  include 
  progressive 
  and 
  regressive 
  sand-waves, 
  as 
  

  

  27 
  P. 
  193 
  ; 
  cf. 
  photograph 
  pi. 
  II, 
  fig. 
  24. 
  

  

  