Yol.  49.]  STEUCTTTEE  OE  THE  WEDLOCK  LIMESTONE.  239 
(iii)  Slides  from  the  Nodular  Beds. 
Slide  Xo.  1. — Xumerous,  very  fragmentary  remains  of  organisms, 
including  polyzoa,  ossicles  of  crinoids,  valves  of  ostracoda,  and 
■several  other  remnants.  There  is  also  a  quantity  of  anisotropic 
mineral  matter,  probably  detrital. 
Slide  Xo.  2. — In  this  the  organic  remains  are  larger  than  those 
noticed  in  No.  1.  They  are  those  of  polyzoa,  small  fragments  of 
shell,  and  a  variety  of  Girvanella. 
Slide  Xo.  3. — The  nodule  from  which  this  slide  was  made  was 
selected  as  representative  of  the  smallest  type  of  nodules,  and  has  a 
maximum  diameter  of  2-20  centimetres.  In  the  centre  there 
is  a  nucleus,  the  original  nature  of  which  is  not  easy  to  deter¬ 
mine.  Around  this  there  is  an  immense  number  of  very  frag¬ 
mentary  calcareous  remains,  cemented  together,  apparently  by 
extremely  fine  material  of  detrital  origin.  Among  the  organic 
fragments  are  portions  of  crinoids  and  tubules  of  Girvanella  ;  but 
the  great  majority  of  the  organic  remains  are  too  fragmentary  to 
be  determined. 
Slide  Xo.  4. — This  is  representative  of  the  irregularly-bedded 
limestones.  It  shows  a  quantity  of  detrital  material  enclosing  a 
rather  large  fragment  of  shell,  and  numerous  other  remains  too 
obscure  to  be  determined.  This  bed  yielded  17*3  per  cent,  of 
residue  insoluble  in  hydrochloric  acid.  The  insoluble  residue  con¬ 
sists  of  small  grains  of  quartz,  mica,  and  cryptocrystalline  siliceous 
aggregations.  There  is  also  a  still  finer  residue  which  is  little 
else  than  a  siliceous  paste ;  it  appears  to  have  originated  from  the 
breaking-up  of  the  last-enumerated  material  during  the  process  of 
boiling  with  acid. 
(iv)  Summary  of  the  Evidence  obtained  from  the 
I Venlock  Limestone  at  May  Hill. 
The  evidence  obtained  from  the  slides  shows  that  the  Massive 
Limestone  at  the  base  is  largely  made  up  of  the  remains  of  crinoids, 
polyzoa,  valves  of  ostracoda,  portions  of  shell,  and  tubules  of  Girva¬ 
nella ,  the  latter  sometimes  forming  oolitic  spherules. 
The  Thin-bedded  Limestone  Series  differs  from  the  Massive 
Limestone,  inasmuch  as  it  contains  a  smaller  proportion  of  crinoid- 
remains  and  a  larger  proportion  of  polyzoa.  Remarkably  fine  forms 
of  Girvanella  are  seen  in  it,  and  to  them  I  shall  refer  later  on. 
The  Xodular  and  Irregularly-bedded  Limestones,  constituting 
the  upper  division,  are  very  arenaceous  and  argillaceous.  The  cal¬ 
careous  element  is  made  up  of  remains  of  organisms  similar  to  those 
mentioned  in  the  beds  below,  but  for  the  most  part  they  are  more 
fragmentary. 
The  most  interesting  result  of  the  microscopic  study  of  these 
rocks  was  the  discovery  of  new  and  interesting  forms  of  Girvanella , 
and  the  fact  that  this  organism  has  taken  so  important  a  part  in 
building  up  the  limestone.  In  PI.  VI.,  figs.  1, 2,  3,  4  a  .and  4  6,  are 
represented  the  forms  which  have  been  discovered. 
