ggQ  MR.  E.  RTJTLEY  ON  THE  DWINDLING  AND  [Aug.  1 893, 
line  limestone  being  more  coherent  than  the  shales  and  consequently 
less  liable  to  disintegration  by  mechanical  agency. 
"  Nodular  conditions  are  to  be  sought  more  among  thin-  than  among 
thick-bedded  limestones.  In  the  latter,  the  residual  nodules  derived 
from  one  bed  would  become  completely  dissolved  before  the  next  bed 
became  sufficiently  thin  to  assume  a  nodular  condition.  This  is 
indicated  in  the  diagram,  PI.  XVTII.  fig.  /.  Where  large  fossils 
are  present  in  a  thick -bedded  limestone,  the  latter  is  moie  likely  to 
weather  into  irregularly  eroded  blocks,  such  as  the  ‘rockery -stones’ 
of  the  Carboniferous  Limestone,  than  to  pass  into  the  condition  of 
smooth  nodules. 
[When  this  paper  was  read,  some  details,  were  given  concerning 
the  relative  thicknesses  of  limestones  in  various  formations,  and  in 
different  localities,  but  it  was  found  so  difficult  to  obtain  satisfactory 
data,  and  the  discrepancy  of  opinion  appeared  to  be  so  great 
concerning  the  probable  origin  of  certain  nodular  conditions,  that 
the  publication  of  all  such  notes  has  been  abandoned,  and  this  moie 
especially  since  the  conditions  which  occur  in  one  district  or  country 
are  not  necessarily  repeated  in  another.  It  has  not  been  the.purpose 
of  this  paper  to  enter  into  a  discussion  of  the  conditions  which  may 
have  favoured  or  retarded  the  formation  of  limestones.  No  doubt 
the  deposition  of  sediment  within  certain  areas  may,  as  Prof.  PIull 
has  pointed  out,  have  acted  as  a  check  to  the  formation  of  limestones, 
hut  there  are  geographical,  bathymetrical,  climatic,  and  other  con¬ 
ditions  which  cannot  be  overlooked  in  a  question  of  this  nature  and 
the  discussion  of  which  could  not  have  been  attempted,  even  in 
outline,  in  the  present  paper.— April  29th,  1893.] 
Conclusions. 
1.  That  bands  of  limestone-nodules  may  in  certain  cases  represent 
what  were  originally  beds  of  limestone. 
2.  That  the  earlier  stages  of  solution  of  a  bed  of  jointed  limestone 
result  in  a  widening  of  the  joints,  or  a  wider  spacing  of  the  blocks 
which  constitute  the  bed,  and  produce  a  certain  degree  of  rounding 
of  the  edges  and  solid  angles  of  each  block. 
3.  That  the  later  stages  of  solution  result  in  nodules,  the  form  ot 
the  nodule,  if  the  limestone  be  tolerably  homogeneous,  being  more 
or  less  closely  related  to  the  original  form  of  the  block  from  which 
it  has  been  derived,  one  nodule  being  derived  from  one  block. 
4.  That  a  limestone-block  of  irregular  form,  or  which  is  not  of 
uniform  texture,  may  result  in  more  than  one  nodule,  and  those, 
perhaps,  of  very  irregular  shape.  .  . 
5.  That  nodular  bands,  occurring  at  the  base  of  a  series  ot  lime¬ 
stone-beds,  may  have  been  preceded,  occurring  at.  the  top  of  a 
series  may  have  been  succeeded,  by  other  beds  of  limestone  which 
have  completely  disappeared. 
6.  That  bands  or  nodules  of  chert  may  represent  all  that 
remains  of  what  were  once  beds  of  cherty  limestone. 
7.  That  the  present  thicknesses  of  limestones  may  in  some  cases 
