﻿S20 
  OLDHAM: 
  GREAT 
  EARTHQUAKE 
  OF 
  1807. 
  

  

  is 
  more 
  important, 
  so 
  complete 
  a 
  check 
  to 
  lateral 
  movement 
  at 
  the 
  

   latter, 
  as 
  would 
  account 
  for 
  the 
  observed 
  rotations 
  in 
  many 
  cases. 
  

  

  There 
  remains 
  but 
  the 
  first 
  mentioned 
  explanation^ 
  that 
  of 
  

   vorticose 
  motion, 
  and 
  with 
  regard 
  to 
  this 
  it 
  seems 
  that 
  the 
  objections 
  

   raised 
  are 
  based 
  on 
  an 
  unnecessarily 
  restricted 
  interpretation 
  of 
  the 
  

   term. 
  It 
  has 
  been 
  supposed 
  necessarily 
  to 
  imply 
  a 
  rotation 
  round 
  an 
  

   axis, 
  by 
  which 
  a 
  similar 
  rotary 
  or 
  top 
  like 
  movement 
  is 
  given 
  to 
  the 
  

   objects 
  rotated. 
  

  

  This 
  is 
  evident 
  in 
  Darwin's 
  objection 
  to 
  the 
  theory, 
  and 
  is 
  even 
  

   more 
  forcibly 
  put 
  by 
  Mallet, 
  who 
  wrote 
  1 
  :— 
  

  

  " 
  The 
  sagacity 
  of 
  Darwin 
  showed 
  him 
  that 
  the 
  vorticose 
  hypothesis 
  was 
  im- 
  

   probable, 
  and 
  that 
  in 
  order 
  to 
  its 
  being 
  at 
  all 
  tenable, 
  a 
  separate 
  vertex 
  must 
  be 
  

   admitted 
  for 
  every 
  separate 
  stone 
  found 
  twisted, 
  the 
  axis 
  of 
  rotation 
  of 
  the 
  vortex 
  

   having 
  been 
  coincident 
  with 
  that 
  of 
  the 
  stone. 
  Besides 
  this 
  paramount 
  improba- 
  

   bility, 
  therefore, 
  a 
  little 
  further 
  reflection 
  would 
  have 
  led 
  either 
  Lyell 
  or 
  Darwin 
  to 
  

   estimate 
  the 
  inconceivable 
  angular 
  velocity 
  of 
  motion 
  at 
  the 
  extremity 
  of 
  the 
  

   radius 
  of 
  one 
  of 
  these 
  vortics, 
  even 
  if 
  assumed 
  at 
  no 
  more 
  than 
  a 
  few 
  hundred 
  

   feet, 
  necessary 
  in 
  order 
  that 
  its 
  velocity 
  within 
  a 
  few 
  inches 
  of 
  the 
  centre 
  should 
  

   be 
  so 
  great 
  as 
  to 
  wrench 
  out 
  of 
  its 
  mortared 
  bed, 
  and 
  twist 
  a 
  block 
  of 
  masonry 
  

   by 
  merely 
  its 
  own 
  inertia." 
  

  

  Here 
  we 
  have 
  the 
  assumption 
  that 
  what 
  is 
  called 
  vorticose 
  

   motion 
  must 
  necessarily 
  be 
  a 
  twisting 
  round 
  an 
  axis, 
  and 
  the 
  

   absurdity 
  to 
  which 
  it 
  leads, 
  both 
  clearly 
  expressed. 
  

  

  But 
  though, 
  interpreted 
  in 
  this 
  way, 
  the 
  term 
  vorticose 
  leads 
  to 
  an 
  

   untenable 
  hypothesis 
  it 
  must 
  not 
  be 
  forgotten 
  that, 
  while 
  popular 
  

   interpretations 
  of 
  natural 
  phenomena 
  are 
  frequently 
  incorrect, 
  they 
  

   almost 
  invariably 
  represent 
  a 
  real 
  substratum 
  of 
  fact* 
  That 
  the 
  

   vorticose 
  should 
  have 
  been 
  for 
  generations 
  regarded 
  as 
  a 
  distinct 
  

   type 
  of 
  earthquake 
  movement 
  points 
  to 
  there 
  being 
  a 
  real 
  difference 
  

   between 
  it 
  and 
  the 
  types 
  which 
  are 
  classified 
  as 
  ' 
  horizontal/ 
  * 
  undu- 
  

   lating* 
  or 
  * 
  palpitating/ 
  Abandoning 
  the 
  restricted 
  interpretation, 
  it 
  

   is 
  not 
  difficult 
  to 
  see 
  that 
  it 
  might 
  well 
  be 
  applied 
  to 
  movement 
  of 
  a 
  

   totally 
  different 
  character, 
  that 
  is 
  to 
  a 
  movement 
  of 
  the 
  wave- 
  

  

  1 
  Jour. 
  Geol.Soc. 
  Dublin, 
  III, 
  138 
  (1845). 
  

   ( 
  220 
  ) 
  

  

  