V ol.  49. ]  STRUCTURE  OE  THE  WENLOCK  LIMESTONE.  243 
“  when  completely  developed,  this  group  of  rocks  [i.  e.  the  Wenlock 
Limestone]  is  of  considerable  thickness,  and  appears  in  two,  three, 
or  more  stages,  alternating  with  shales,  and  occupying,  with  these, 
altogether  as  much  as  280  feet  of  thickness.” 1  In  the  section  which 
I  have  given  of .  Biddulph’s  Quarry  at  Ledbury  there  is  only 
46  feet  .8  inches  of  strata,  and  this  is  the  greatest  development  that 
I  have  met  with.  It  is,  however,  exceedingly  probable  that  Prof. 
Phillips’s  statement  is  correct,  for  when  he  surveyed  the  district 
the  limestone  was  much  more  extensively  worked  for  lime-burning 
than  is  now  the  case  ;  and,  consequently,  he  was  better  able  to 
arrive  at  a  correct  estimation  of  the  maximum  thickness  than  any 
observer  at  the  present  day. 
Slides  from  the  Ledbury  Limestone  (ls£  Quarry). 
The  Slate-coloured  Nodular  Limestone  at  the  base  of  the  section 
contains  as  much  as  304  per  cent,  of  residue  insoluble  in  hydro¬ 
chloric  acid.  This  residue  is  made  up  of  very  small  flakes  of  mica 
and  quartz,  with  a  quantity  of  amorphous  and  cryptocrystalline 
siliceous  aggregations,  and  pyrites. 
The  calcareous  portion  consists  of  valves  of  ostracoda,  some  of 
them  well  preserved,  ossicles  of  crinoids,  fragments  of  shell,  and 
polyzoa.  As  a  whole  this  limestone  is  exceedingly  compact,  and 
there  is  little  infilling  calcite. 
The  Crystalline  Limestone  which  follows  contains  a  great  quantity 
of  organic  fragments,  and  only  4  per  cent,  of  residue  insoluble  in 
hydrochloric  acid.  Among  the  organic  fragments  are  those  of  shells 
and  polyzoa,  and  some  few  ossicles  of  crinoids.  These  remains  of 
organisms  are,  on  the  whole,  well  preserved,  and  the  crystalline 
nature  of  the  rock  arises  from  the  quantity  of  infilling  calcite. 
The  Dark  Limestone,  No.  3  in  the  section  (see  p.  242),  is  very 
hard  and  compact,  with  little  infilling  calcite.  It  contains  13*9  per 
cent,  of  residue  insoluble  in  hydrochloric  acid.  This  residue  is 
made  up  of  a  quantity  of  amorphous  and  cryptocrystalline  siliceous 
aggregations,  some  little  felspar,  and  a  paste  full  of  crystallites, 
which  originates  from  the  breaking  up  of  the  cryptocrystalline 
matter.  The  organic  fragments  are  chiefly  ossicles  of  crinoids,  with 
some  portions  of  shell  and  valves  of  ostracoda. 
The  nodules  in  Bed  No.  6  contain,  like  the  Dark  Limestone,  13*9 
per  cent,  of'  insoluble  residue,  made  up  of  the  same  material  as  the 
residue  in  the  beds  below.  The  calcareous  portion  consists  of  very 
fragmentary  remains  of  crinoids,  shells,  and  a  few  broken  valves  of 
ostracoda.  In  addition,  however,  there  are  a  few  aggregations  of 
Girvanella  problematica  which,  strange  to  say,  have  not  been  noticed 
in  the  limestones  below. 
The  nodules  which  occur  in  the  uppermost  Argillaceous  Beds 
contain  as  much  as  20  per  cent,  of  residue  insoluble  in  hydrochloric 
acid,  and  the  calcareous  portion  is  made  up  of  very  obscure  frag¬ 
ments  of  shell  and  crinoids,  etc. 
1  Op.  cit.  p.  78. 
