Vol.  49.] 
DISAPPEARANCE  OF  LI3IESTONES. 
373 
If  the  beds  were  horizontal  or  inclined  at  a  low  angle  and  the 
removal  more  or  less  complete,  4  creeps  ’  would  occur,  and  finally 
the  bed  which  originally  rested  upon  the  limestone  would  come  in 
contact  with  the  upper  surface  of  the  bed  upon  which  the  limestone 
rested. 
[In  the  discussion  Svhich  followed  the  reading  of  this  paper,  the 
question  of 4  creeps  ’  was  raised,  the  absence  of  disturbance  in  the  beds 
which  might  once  have  rested  upon  or  have  supported  a  bed  or  a 
series  of  beds  of  limestone  being  adduced  as  evidence  that  the 
removal  of  such  beds  by  the  action  of  solvents  did  not  occur  either 
commonly  or  on  a  large  scale.  To  this  it  may  be  answered  that 
4  creeps 5  would  certainly  occur,  but  that  they  would  be  comparatively 
inappreciable  when  contrasted  with  those  brought  about  by  mining 
operations.  Furthermore,  the  removal  of  a  limestone  by  water 
charged  with  carbonic  acid  is  a  slow  and  gradual  process  compared 
with  the  dissolving  of  beds  of  rock-salt  or  the  operations  of  the 
miner,  and,  although  the  principle  involved  is  the  same  in  both  cases, 
yet  the  action  in  the  one  instance  differs  in  degree  from  that 
in  the  other.  The  sand-grains  gently  trickling  in  an  hourglass  and 
the  sliding  and  tumbling  masses  in  a  landslip  afford  examples  of 
two  very  different  phenomena  dependent  upon  the  same  principle, 
namely  the  gravitation  of  matter  upon  smooth  and  sufficiently  in¬ 
clined  surfaces.  In  the  earlier  stages  of  the  dwindling  of  a  bed  of 
jointed  limestone,  the  widening  of  the  joints  is  comparatively  slight. 
It  is  when  a  limestone-bed  has  been  reduced  to  about  half  its  original 
thickness  that  we  have  a  condition  which,  on  a  diminutive  scale, 
resembles  the  4  pillar-and-stall  ’  work  in  a  coal-mine,  and  it  is  at  this 
stage  that  4  creeps  ’  and  4  sits  ’  will  become  most  marked.  As  the 
removal  of  the  limestone  continues  the  nodules  will  become  thinner 
and  more  lenticular,  and  the  flexures  of  the  superincumbent  and 
subjacent  beds  will  diminish.  As  the  nodules  become  smaller  and 
thinner,  these  flexures  (or  4  creeps  and  sits  ’)  will  become  more  and 
more  flattened  by  pressure  of  overlying  rock  until,  when  the 
nodules  have  wholly  disappeared,  the  once  overlying  and  underlying 
beds  come  into  unbroken  contact,  the  flexures  are  smoothed  out,  and 
any  comminuted  rock-matter,  which  may  have  resulted  from 
cracking  consequent  upon  flexure,  will  become  reconsolidated,  by 
pressure,  into  the  general  planes  of  stratification. 
Under  such  circumstances,  no  evidence  would  remain  of  the  former 
existence  of  the  limestone-bed,  save  perhaps  in  the  more  calcareous 
nature  of  the  adjacent  strata,  through  which  water,  holding  calcium 
bicarbonate  in  solution,  may  have  filtered,  in  the  presence  of  chert 
which  the  limestone  might  have  contained,  or  in  the  presence  of 
silica  or  other  comparatively  insoluble  substance  by  which  the 
limestone  might  be  replaced. — April  29th,  1893.] 
In  the  case  of  a  limestone  interstratified  with  highly-inclined  or 
vertical  beds,  the  fissure,  caused  by  the  removal  of  the  limestone, 
would  either  become  closed  by  earth-movements  bringing  the  walls 
