﻿432 
  Kindle 
  — 
  Factor 
  in 
  Rounding 
  of 
  Sand 
  Grains. 
  

  

  operation 
  of 
  the 
  agency 
  to 
  be 
  described 
  it 
  will 
  be 
  seen 
  that 
  

   the 
  limitation 
  on 
  rounding 
  imposed 
  according 
  to 
  Daubree 
  

   by 
  small 
  size 
  largely 
  disappears. 
  

  

  None 
  of 
  the 
  numerous 
  geological 
  papers 
  dealing 
  with 
  

   this 
  subject, 
  which 
  are 
  known 
  to 
  the 
  writer, 
  consider 
  any 
  

   factors 
  other 
  than 
  wind 
  and 
  water 
  in 
  discussing 
  the 
  

   rounding 
  of 
  sand 
  grains. 
  4 
  A 
  third 
  factor 
  which 
  the 
  

   writer 
  believes 
  to 
  be 
  of 
  some 
  importance 
  is 
  the 
  agency 
  of 
  

   certain 
  invertebrates 
  in 
  triturating 
  sand 
  grains 
  within 
  

   their 
  digestive 
  tracts. 
  Certain 
  echinoderms, 
  notably 
  the 
  

   sea-urchins, 
  feed 
  upon 
  sandy 
  sediments 
  and 
  the 
  diatoms, 
  

   sea- 
  weed 
  and 
  other 
  organic 
  materials 
  which 
  may 
  be 
  asso- 
  

   ciated 
  with 
  sea 
  sand. 
  Various 
  naturalists 
  have 
  noted 
  

   the 
  peculiar 
  feeding 
  habits 
  of 
  echinoderms 
  which 
  leads 
  

   them 
  to 
  eat 
  sand. 
  Scott 
  5 
  has 
  given 
  the 
  following 
  account 
  

   of 
  his 
  observations 
  on 
  the 
  feeding 
  habit 
  of 
  sea-urchins 
  

   in 
  the 
  Bay 
  of 
  Fundy: 
  

  

  "When 
  the 
  urchins 
  came 
  from 
  localities 
  remote 
  from 
  

   seaweed 
  the 
  excrements 
  were 
  the 
  small 
  globular 
  masses 
  

   such 
  as 
  are 
  observed 
  in 
  the 
  alimentary 
  tract. 
  In 
  tide 
  

   pools 
  where 
  sea-urchins 
  are 
  abundant, 
  the 
  bottom 
  is 
  fre- 
  

   quently 
  covered 
  with 
  a 
  layer 
  of 
  the 
  castings 
  of 
  these 
  

   animals 
  ... 
  In 
  only 
  a 
  few 
  cases 
  was 
  sea-weed 
  observed 
  

   in 
  the 
  intestines 
  of 
  the 
  urchins 
  which 
  had 
  been 
  dredged 
  

   in 
  the 
  deeper 
  waters 
  of 
  the 
  bay. 
  In 
  their 
  case, 
  as 
  in 
  the 
  

   case 
  of 
  urchins 
  living 
  on 
  rocks 
  devoid 
  of 
  sea-weed, 
  the 
  

   digestive 
  tract 
  contained 
  chiefly 
  the 
  globular 
  masses 
  of 
  

   surface 
  sand. 
  ... 
  It 
  feeds 
  partly 
  on 
  diatoms 
  and 
  other 
  

   small 
  algae, 
  &c, 
  which 
  it 
  cuts 
  from 
  the 
  rocks 
  with 
  the 
  

   sharp 
  points 
  of 
  its 
  teeth 
  but 
  it 
  is 
  also 
  fond 
  of 
  dead 
  fishes 
  

   which 
  are 
  soon 
  devoured, 
  bones 
  and 
  all, 
  by 
  it 
  in 
  the 
  Bay 
  

   of 
  Fundy. 
  " 
  "The 
  sea-urchin 
  has 
  thus 
  two 
  principal 
  

   foods 
  which 
  we 
  may 
  call 
  sea-weed 
  and 
  surface 
  sand." 
  

  

  Prof. 
  Verrill 
  6 
  found 
  sea-urchins 
  to 
  be 
  very 
  efficient 
  

   agents 
  in 
  reducing 
  to 
  small 
  fragments 
  the 
  great 
  variety 
  

   of 
  sea 
  shells 
  found 
  in 
  the 
  Bermudas. 
  He 
  states 
  that 
  "the 
  

   shells 
  on 
  the 
  average 
  constitute 
  about 
  80 
  to 
  90 
  per 
  cent 
  

   of 
  the 
  whole 
  mass 
  (of 
  sand), 
  limestone 
  detrites 
  perhaps 
  

   5 
  per 
  cent. 
  The 
  shells 
  are 
  mostly 
  recently 
  dead. 
  Their 
  

   generally 
  broken 
  condition 
  (fig. 
  9) 
  is 
  due 
  to 
  the 
  fact 
  that 
  

  

  * 
  A 
  paper 
  on 
  the 
  rounding 
  of 
  grains 
  of 
  sand 
  by 
  solution 
  bv 
  J. 
  J. 
  Galloway- 
  

   is 
  contained 
  in 
  the 
  April 
  number 
  of 
  this 
  Journal, 
  47, 
  pp. 
  270-280 
  — 
  Editors. 
  

  

  5 
  Scott, 
  Dr. 
  F. 
  H. 
  : 
  Food 
  of 
  the 
  Sea-Urchin. 
  Contr. 
  Can. 
  Biology 
  1901, 
  

   Suppl. 
  to 
  32nd 
  Ann. 
  Kept. 
  V, 
  pp. 
  50, 
  51, 
  52. 
  

  

  6 
  Verrill, 
  A. 
  E. 
  : 
  Notes 
  on 
  Geologv 
  of 
  the 
  Bermudas, 
  this 
  Journal, 
  9, 
  

   p. 
  330, 
  1900. 
  

  

  