372 
ME.  E.  KTJTLEY  OX  THE  DWINDLING  AND 
[Aug.  1893, 
31.  On  the  Dwindling  and  Disappearance  of  Limestones.  By 
Prank  Butley,  Esq.,  E.G.S.,  Lecturer  on  Mineralogy  in  the 
Bo}Tal  College  of  Science,  London.  (Bead  April  12th,  1893.) 
[Abridged.] 
[Plate  XYIIL] 
There  are  probably  few  instances  in  nature  in  which  limestone- 
beds  are  so  protected  that  water  cannot  gain  access  to  them.  A 
limestone-bed  to  which  water  charged  with  carbonic  acid  gains 
access  becomes  gradually  dissolved,  and,  furthermore,  the  solvent 
action  of  humus  acids  must  also,  in  some  cases,  be  taken  into 
account.1 2  The  question  whether  such  a  bed  will  completely  vanish 
is  one  which  involves  merely  the  magnitude  of  the  bed,  the  duration 
and  energy  of  the  solvent  action,  and  the  freedom  of  the  limestone 
from  foreign  matter  of  a  more  or  less  insoluble  nature.  If  unlimited 
time  be  conceded,  there  seems  no  reason  why  very  thick  beds  of 
limestone  should  not  wholly  disappear  ;  at  all  events  thin  ones  may 
easily  do  so. 
The  formation  of  caves,  chasms,  and  pinnacles,  the  general  sculp¬ 
turing  of  limestones,  and  the  thick  deposits  of  calcareous  tufa  which 
occur  in  many  localities  sufficiently  attest  the  activity  with  which 
the  erosion  of  limestones  has  been  carried  on  in  recent  times,'  and 
there  appears  to  be  no  reason  to  doubt  that  similar  work  has  been 
constantly  in  progress  during  bygone  ages,  under  like  conditions. 
Given  like  conditions,  the  greater  the  age  of  any  limestone-deposit, 
the  more  will  it  have  been  wasted  away.  Granted  sufficient  time, 
its  disappearance  is  inevitable. 
Any  argument  adduced  in  support  of  the  probable  disappearance 
of  very  ancient  beds  of  limestone  may  be  applied  with  additional 
force  in  the  cases  of  rock-salt  and  g}Tpsum.3 
Where  limestones  occur  at  the  surface,  their  erosion  is  due  not 
only  to  chemical,  but  also  to  mechanical  natural  agencies,  the  latter 
being  likewise  important  factors. 
In  the  case  of  a  limestone-bed  occurring  between  rocks  of  a 
different  character  the  erosion  of  the  limestone  is  quite,  or  almost 
wholly,  dependent  upon  the  infiltration  of  water  charged  with  car¬ 
bonic  acid,  or  other  solvent.  The  partial  or  entire  removal  of  inter- 
bedded  limestones  must,  probably,  in  many  cases  have  taken  place 
in  this  manner  during  the  lapse  of  ages. 
1  Alexis  A.  Julien,  ‘  On  tie  Geological  Action  of  the  Humus  Acids,’  Proc. 
Amer.  Assoc,  vol.  xxviii.  (1879,  Saratoga  Meeting)  ;  sep.  cop.  Salem,  1880. 
2  Credner  cites  an  instance  in  which,  in  one  locality  alone,  the  limestone- 
rocks  yield,  in  one  year,  sufficient  calcareous  tufa  to  form  a  cube  measuring  over 
33  metres  (35§  yards)  on  the  side,  ‘Elemente  der  Geologie,’  3rd  eel.  (1870) 
p.  188. 
3  Gypsum  is  soluble  in  460  times  its  weight  of  water,  and  limestone  in  about 
1000  of  w’ater  charged  with  carbonic  acid. 
