﻿of 
  various 
  Substances 
  on 
  Solidification. 
  

  

  233 
  

  

  into 
  any 
  detail 
  to 
  prove 
  that 
  the 
  phenomena 
  are 
  due 
  to 
  the 
  contrac- 
  

   tion 
  of 
  the 
  already 
  solidified 
  exterior 
  upon 
  the 
  unyielding 
  interior 
  of 
  the 
  

   mass 
  ; 
  the 
  former 
  becoming 
  fractured 
  by 
  its 
  own 
  grip, 
  and 
  its 
  material 
  

   being 
  highly 
  elastic, 
  often 
  yields 
  with 
  apparently 
  explosive 
  violence 
  like 
  

   a 
  suddenly 
  broken 
  spring 
  (see 
  fig. 
  9, 
  which 
  shows 
  the 
  appearance 
  of 
  one 
  

   of 
  these 
  fractured 
  and 
  slowly 
  exuding 
  blocks). 
  

  

  [The 
  following 
  remarks 
  may 
  be 
  made, 
  in 
  addition 
  to 
  those 
  preceding, 
  

   in 
  contravention 
  of 
  the 
  supposed 
  expansion 
  of 
  slags 
  or 
  lavas 
  in 
  consoli- 
  

   dating. 
  It 
  is 
  well 
  known 
  that 
  masses 
  of 
  mud 
  when 
  dried 
  by 
  the 
  sun 
  

   crack, 
  the 
  fissures 
  penetrating 
  nearly 
  perpendicular 
  from 
  the 
  surface 
  and 
  

   separating 
  into 
  more 
  or 
  less 
  symmetrical 
  prisms. 
  Blocks 
  of 
  starch 
  after 
  

   desiccation 
  present 
  similar 
  phenomena, 
  which 
  are 
  also 
  frequently 
  seen 
  

   exemplified 
  by 
  the 
  uppermost 
  beds 
  of 
  argillaceous 
  limestone 
  (or 
  calp) 
  of 
  

   Ireland 
  when 
  first 
  laid 
  bare 
  from 
  its 
  detrital 
  covering. 
  In 
  all 
  these 
  cases 
  

   there 
  can 
  be 
  no 
  doubt 
  that 
  the 
  phenomena 
  are 
  due 
  to 
  the 
  shrinkage 
  of 
  

   the 
  mass 
  in 
  drying. 
  But 
  shrinkage 
  or 
  contraction 
  by 
  cooling 
  and 
  consoli- 
  

   dation 
  ought 
  to 
  present 
  us 
  with 
  like 
  results 
  ; 
  and 
  these 
  we 
  see 
  actually 
  

   manifest 
  in 
  the 
  splitting-up 
  of 
  basalt 
  into 
  columnar 
  prisms 
  whose 
  long 
  

   axes 
  are 
  always 
  found 
  perpendicular 
  to 
  the 
  surface 
  by 
  which 
  the 
  heat 
  of 
  

   the 
  mass 
  was 
  dissipated. 
  Such 
  columnar 
  separation 
  is 
  not 
  confined 
  to 
  

   basalt 
  ; 
  instances 
  of 
  it 
  are 
  abundant 
  in 
  lavas 
  of 
  every 
  age, 
  the 
  surfaces 
  

   of 
  the 
  prisms 
  in 
  these 
  being 
  sometimes 
  straight, 
  sometimes 
  curved. 
  

   Although 
  much 
  remains 
  yet 
  to 
  be 
  investigated 
  before 
  all 
  the 
  circumstances 
  

   attending 
  the 
  splitting-up 
  of 
  masses 
  of 
  basalt 
  or 
  lava 
  can 
  be 
  said 
  to 
  be 
  

   fully 
  understood, 
  jet 
  enough 
  is 
  already 
  known 
  and 
  clearly 
  explained 
  to 
  

   make 
  it 
  certain 
  that 
  it 
  is 
  due 
  to 
  contraction 
  of 
  these 
  materials 
  as 
  they 
  

   cool 
  ; 
  and 
  that 
  this 
  form 
  of 
  splitting-up 
  is 
  wholly 
  incompatible 
  with 
  that 
  

   of 
  any 
  Assuring 
  that 
  could 
  arise 
  from 
  the 
  refrigeration 
  of 
  a 
  mass 
  the 
  

   volume 
  of 
  every 
  part 
  of 
  which 
  expanded 
  in 
  consolidating.] 
  

  

  As 
  in 
  what 
  precedes 
  the 
  hypothesis 
  upon 
  which 
  the 
  lunar 
  volcanic 
  

   theory 
  of 
  Messrs. 
  Nasinyth 
  and 
  Carpenter 
  rests 
  is 
  proved 
  to 
  be 
  without 
  

   foundation, 
  it 
  seems 
  needless 
  to 
  enlarge 
  upon 
  the 
  incongruities 
  and 
  con- 
  

   tradictions 
  which 
  the 
  theory 
  itself 
  presents 
  when 
  fairly 
  applied 
  to 
  such 
  

   knowledge 
  as 
  we 
  have 
  of 
  the 
  volcanic 
  features 
  of 
  the 
  moon, 
  or 
  still 
  more 
  

   when 
  applied, 
  as 
  it 
  must 
  be 
  were 
  it 
  true, 
  to 
  those 
  of 
  our 
  earth, 
  [assuming 
  

   the 
  materials 
  of 
  our 
  earth 
  and 
  satellite 
  analogous 
  in 
  their 
  physical 
  and 
  

   chemical 
  properties 
  — 
  an 
  assumption 
  made 
  by 
  these 
  authors 
  throughout 
  

   their 
  work, 
  though 
  without 
  any 
  attempt 
  to 
  support 
  it 
  by 
  proof]. 
  

  

  In 
  concluding 
  this 
  paper, 
  the 
  author 
  has 
  to 
  express 
  his 
  thanks 
  for 
  the 
  

   liberality 
  and 
  assistance 
  afforded 
  him 
  by 
  Messrs. 
  Maudslay, 
  Sons, 
  and 
  

   Field, 
  who 
  showed 
  their 
  just 
  appreciation 
  of 
  the 
  true 
  value 
  of 
  scientific 
  

   research 
  by 
  assisting 
  in 
  this 
  inquiry 
  of 
  an 
  abstract 
  character, 
  and 
  with- 
  

   out 
  apparent 
  technical 
  applicability. 
  He 
  also 
  has 
  to 
  thank 
  Mr. 
  E. 
  

   Duncan, 
  of 
  the 
  above 
  firm, 
  for 
  his 
  personal 
  aid 
  and 
  cooperation. 
  He 
  

   also 
  has 
  to 
  express 
  his 
  thanks 
  for 
  the 
  valuable 
  assistance 
  so 
  readily 
  

  

  