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MR.  E.  WETHERED  ON  THE  MICROSCOPIC 
[May  i893r 
calcareous  fragments  tried,  as  it  were,  to  accumulate,  but  that  the 
process  was  interrupted,  the  fragments  were  rolled  about  with 
sediment,  and  hence  arose  the  nodules. 
The  remains  of  crinoids  enter  largely  into  the  structure  of  these 
limestones.  In  making  this  statement  I  am  not  in  accord  with  the 
late  Prof.  Phillips,  who,  referring  to  the  Wenlock  Limestone,  re¬ 
marked  that  “it  is  rarely  composed  of  fragments  of  crinoidal 
columns.”  1  Thin  slides  of  the  limestone,  however,  show  that  cri- 
noid-remains  are  abundant,  but  they  are  very  fragmentary,  and 
for  the  most  part  small.  Shell-fragments  come  next  in  importance, 
then  valves  of  ostracoda,  and  lastly  polyzoa,  more  especially  in  the 
thin  beds  at  May  Hill. 
The  organism  known  as  Girvanella  has  contributed  largely  to 
some  of  the  beds  at  May  Hill  and  Purley,  and  the  process  seems  to 
have  been  as  follows  : — Fragments  of  organisms  were  deposited  on 
the  sea-floor ;  around  these  the  Girvcmella- tubules  collected,  some¬ 
times  entirely  enclosing  a  fragment  with  a  crust  of  tubules,  and 
thus  giving  rise  to  a  spherule  or  granule,  the  determination  of  , 
which  depended  on  the  shape  of  the  fragment  enclosed.  To  such 
an  extent  did  this  process  go  on  that,  in  some  of  my  slides,  almost 
every  fragment  is  either  enclosed  or  has  some  tubules  attached  to  it. 
It  is  curious  to  note  how  very  local  the  various  forms  of  Girvan- 
ella  are.  Thus  some  of  the  thin-bedded  limestones  at  May  Hill  seem 
to  have  been  deposited  under  conditions  especially  favourable  to 
the  growth  of  certain  forms  of  Girvanella ,  represented  in  PL  VI. 
figs.  1,  2,  and  3.  These  have  not  been  noticed  in  the  beds  at  Purley  ; 
but  on  the  other  hand  a  form  appears  there  (PI.  VI.  fig.  5)  which 
has  not  been  found  at  May  Hill. 
Girvanella  problematica  seems  to  constitute  an  exception  to  what 
I  have  just  stated,  and  to  be  a  most  persistent  form.  It  occurs  in 
the  beds  at  May  Hill,  Purley,  and  Martin’s  Quarry,  and  in  the 
nodules  obtained  from  Biddulph’s  Quarry  ;  in  the  two  last-named 
localities  it  is  the  only  Girvanella  found. 
Whether  Girvanella  is  to  be  regarded  as  an  animal  or  a  plant 
is  a  question  which  is  not  absolutely  settled.  Pothpletz  has 
figured2  several  forms  of  fossil  algae,  among  which  he  includes 
Girvanella .  I  certainly  think  that  the  forms  which  I  have  dis¬ 
covered  in  the  Wenlock  Limestone  seem  more  favourable  to  the 
vegetable  theory  of  the  origin  of  this  fossil  than  those  described  in 
my  former  paper,3  and  possibly  it  may  be  allied  to  the  calcareous 
algae  ;  more  than  this,  however,  I  cannot  say.  Further  investigation 
may  throw  light  on  this  interesting  question,  but  whether  it  be  a 
vegetable  or  an  animal  it  is  certainly  a  very  low  form  of  life,  per¬ 
haps  the  lowest  of  which  we  have  knowledge  in  a  fossil  state. 
1  Op.  supra  cit.  p.  78. 
2  See  Zeitschr.  d.  Deutscb.  Geol.  Gesellsch.  for  1891,  p.  295. 
3  Quart.  Journ.  Geol.  Soc.  vol.  xlvi.  (1890)  pi.  xi. 
