-48  MICROSCOPIC!  STRUCTURE  OP  WENLOCX  LIMESTONE.  [May  1 893, 
structure  in  the  oolitic  and  pisolitic  granules  which  abounded  in  some 
of  these  limestones.  He  agreed  with  the  Author  in  believing  that 
the  large  pisolite-grains,  at  least,  were  probably  all  due  to  Girvanella , 
although  in  many  of  them  the  organic  characters  had  been  sub¬ 
sequently  obliterated.  With  respect  to  the  nature  of  Girvanella ,  the 
speaker  considered  that  Dr.  Rothpletz  had  satisfactorily  shown  its 
relationship  to  certain  forms  of  fossil  and  recent  calcareous  algae. 
Mr.  Clement  Reid  suggested  that  these  tubes  might  be  formed  in 
a  variety  of  ways,  and  might  not  be  due  to  the  agency  of  any  special 
organism.  He  thought  it  probable  that  many  of  them  were  merely 
inorganic  encrustations  on  any  filamentous  plants,  such  as  algae, 
growing  in  water  containing  much  lime.  The  tubes  might  be  com¬ 
pared  with  the  deposits  on  the  fibres  of  a  common  patent  apparatus 
a  sort  of  mop — used  to  extract  lime  from  the  water  in  boilers. 
If  the  fibres  within  these  artificial  encrustations  were  to  decay,  there 
would  be  left  a  tangled  mass  of  small  tubes,  like  most  of  the 
so-called  Girvanellce. 
Mr.  Rutley  pointed  out  that  if  the  suggestion  of  Mr.  Clement  Reid 
were  correct,  the  structure  of  Girvanella  would  correspond,  on  a  very 
small  scale,  with  that  of  Osteocolla. 
The  Rev.  H.  Winwooe  said  that  whatever  development  had  taken 
place  in  the  mind  of  the  Author  of  the  paper  as  to  the  character  of 
the  organism,  he  certainly  must  feel  gratified  at  the  progress  of 
development  in  the  views  of  geologists  generally,  and  the  consensus 
of  opinion  as  to  the  organic  nature  of  these  tubules.  He  remem¬ 
bered,  when  the  subject  was  first  brought  before  the  Society,  that 
the  tubules  were  of  a  simpler  character — single  ones  merely,  or 
circling  round  some  nucleus ;  now,  by  the  Author’s  further  researches, 
they  appeared  of  different  sizes  and  shapes.  One  specimen  which 
Mr.  Wethered  had  kindly  sent  him  seemed  to  branch  off  into  a 
wisp-like  form,  which,  as  Dr.  Hinde  had  just  remarked,  looked 
like  an  alga.  He  hojied  that  Mr.  Wethered  would  continue  his 
good  work,  and  bring  further  developments  before  the  Fellows. 
The  Author  replied  that,  as  to  oolitic  structure  in  general  being 
due  to  the  growth  of  Girvanella- tubules,  he  had  proved  to  the  satis¬ 
faction  of  most  people  that  this  was  the  origin  of  pisolite ;  and  it 
would  be  found  to  apply  to  the  smaller  oolitic  granules  to  a  much* 
greater  extent  than  was  generally  supposed. 
In  reply  to  Mr.  Reid  and  Mr.  Rutley,  the  Author  said  that  though 
there  was  doubt  as  to  whether  Girvanella  was  an  animal  or  a  plant, 
there  was  absolutely  none  on  the  question  of  its  being  organic. 
With  the  other  Fellows  who  had  spoken  he  was  in  practical 
agreement,  and  he  thanked  them  all  for  their  remarks. 
