Vol.  49.] 
structure  or  the  svexloce  limesioxe. 
245 
The  Genlock  Limestone  at  Ledbury  is  remarkable  for  the  small 
-variety  of  organisms  which  have  contributed  to  its  formation. 
Crinoidal  remains  are  by  far  the  most  numerous :  next  in  importance 
•come  fragments  of  shell,  valves  of  ostracoda,  and  polyzoa.  The  latter, 
however,  are  not  common,  a  scarcity  which  contrasts  strongly  with 
the  great  number  of  polyzoan  remains  found  at  May  Hill.  Moreover, 
the  almost  entire  absence  of  G-irvaaella  is  remarkable :  occasional 
aggregations  of  Girvanellci  problematic!  have  been  noticed,  but 
the  varieties  seen  at  May  Hill  and  Purlev  are  wanting. 
i  .  Gexeral  Sum mary. 
The  evidence  recorded  in  this  paper  points  to  the  Wenloek  Lime¬ 
stone  as  having  been  deposited  under  varying  local  conditions.  At 
May  Hill,  as  before  stated,  three  successive  stages  are  clearly  de¬ 
fined.  They  are  : — (1)  TThat  I  have  termed  ‘  Massive  Limestone,’ 
at  the  base  of  the  quarry :  (2)  Thin-bedded  Limestones ;  (3) 
Xodular  and  Irregularly-bedded  Series.  These  stages  are  indicated 
at  Purley,  but  are  less  clearly  defined,  and  the  Massive  Bed  at 
the  base  is  here  more  or  less  oolitic.  At  Martin's  Quarrv,  near 
Ledbury,  the  Massive  Limestone  and  Xodular  Beds  do  indeed  occur, 
but  the  Thin-bedded  Limestones  are  absent.  MTth  the  beds  in 
Biddulph’s  Quarry  correlation  is  difficult ;  still  we  have  in  the 
Crystalline  and  Dark  Limestones  ( Xos.  2  &  3)  what  may  be  termed 
Massive  Beds  followed  by  a  thick  development  of  the  Aodular  Series. 
I  have  from  time  to  time,  during  the  course  of  this  paper,  men¬ 
tioned  the  proportion  of  residue  which  is  left  after  boiling  portions  of 
the  limestone  in  hvdrochloric  acid.  This,  to  some  extent,  is  a  e;uide 
to  the  amount  of  detrital  material  deposited  with  the  limestone,  but 
allowance  must  be  made  for  the  disappearance  of  decomposable 
minerals  such  as  felspar.  The  estimations  show  a  larger  proportion 
of  residue  than  is  usual  in  most  limestones,  and  as  there  is  evidence 
that  the  mineral-grains  in  the  original  sediment  have  undergone 
decomposition,  it  is  clear  that  the  amount  of  sediment  deposited 
was  considerable.  The  evidence  of  this  decomposition  is  seen  in 
the  fact  that,  with  the  exception  of  occasional  fragments  of  felspar, 
the  mineral  constituents  still  existing  in  the  residue  are  not  easily 
decomposable.  I  have  now  had  some  considerable  experience  in 
the  examination  of  insoluble  residues,  and  in  my  opinion  the 
amorphous  and  cryptocrystalline  silica  in  the  residues  under  con¬ 
sideration  is  the  residuum  of  decomposed  minerals  such  as  felspars  ; 
the  alkaline  constituents,  of  course,  would  be  removed  by  perco¬ 
lating  waters  before  the  limestones  attained  their  present  com- 
j^actness  and  crystalline  condition.  The  quantity  of  detritus  appears 
to  have  increased  as  the  formation  went  on,  until  so  much  was 
deposited  that  calcareous  organisms  were  unable  to  accumulate,  and 
the  limestone-forming  process  ceased.  This  latter  stage  is  repre¬ 
sented  by  the  Xodular  and  Irregularly-bedded  -Limestone  con¬ 
stituting  the  uppermost  division.  It  would  appear  as  though  the 
