1 1  2  PKOCEEDINGS  OE  THE  GEOLOGICAL  SOCIETV.  [May  1 893, 
with  the  inner  whorls  phospliatized.  Mr.  Teall  had  previously  noted 
the  occurrence  of  Gault  at  West  Dereham.  Prom  this  point  the 
Gault  rapidly  diminishes  southward.  At  Roydon,  which  is  about 
halfway  between  Stoke  Perry  and  Hunstanton,  a  boring  yielded  very 
remarkable  results.  Resting  on  the  Carstone  we  there  have  20  feet 
of  Gault,  the  lower  portion  blue  and  argillaceous,  the  upper  portion 
grey  and  marly ;  towards  the  centre  occur  buff  sub-calcareous  rocks, 
blotched  and  stained  with  red,  which  in  a  neighbouring  section  are 
shown  to  contain  well-known  Gault  Ammonites  and  Inocerami. 
In  the  grey,  marly,  upper  portion  Belemnites  are  abundant. 
Dersingham  is  the  point  where  the  lithological  change  becomes  more 
marked.  In  our  Authors’  map  the  Gault,  regarded  lithologically, 
is  represented  as  ceasing  at  this  village,  and  the  beds  between  the 
Carstone  and  the  base  of  the  Chalk  Marl  are  reduced  to  some  7  feet 
in  all,  as  proved  by  a  boring :  these  beds  are  marls,  greyish  white 
above,  yellowish  towards  the  centre,  and  more  argillaceous  below, 
with  a  tendency  to  redness  in  colour. 
The  next  point  is  to  connect  the  3  feet  of  Red  Rock  at  Hunstanton 
with  the  7  feet  of  Norfolk  Gault,  which  seems  to  end  off  in  the 
manner  above  stated  at  Dersingham.  Pirst  of  all,  there  is  the 
evidence  of  identity  of  position  between  the  Carstone  below  and 
the  equivalents  of  the  so-called  ‘  Sponge-bed  ’  above.  There  is 
no  question  as  to  the  identity  of  the  Carstone  ;  the  only  doubt  which 
could  possibly  arise  relates  to  the  upward  limit,  and  here  the 
Authors  admit  that  their  case  largely  depends  upon  the  exact  correla¬ 
tion  of  the  presumed  equivalents  of  the  Hunstanton  4  Sponge-bed,’ 
which  is  for  them  the  base  of  the  Chalk  Marl,  though  so  unlike 
the  base  of  the  Chalk  Marl  in  other  districts.  On  the  whole,  the 
argument  from  stratigraphical  position  seems  to  point  to  a  lithological 
passage  between  the  Gault  and  the  Red  Chalk.  It  may  indeed  seem 
strange  to  those,  who  have  never  recognized  the  marly  character  of 
much  of  the  Upper  Gault,  that  this  mainly  argillaceous  formation 
should  shrink  to  3  feet  of  Red  Chalk  on  the  eastern  shores  of  the 
AVash,  nor  is  it  exactly  clear  through  what  causes  the  iron  in  the  Red 
Chalk  appears  in  the  state  of  sesquioxide,  while  the  iron  in  the 
Gault  is  mainly  in  the  state  of  protoxide. 
The  fossils  hitherto  found  in  the  Norfolk  Gault  are  not  very 
numerous,  but  nearly  all  are  of  species  which  occur  in  the  Red  Rock  of 
Hunstanton,  and  this  fact,  coupled  with  the  stratigraphical  evidence, 
seems  conclusive  as  to  their  being  mainly  on  the  same  geological 
horizon.  Undoubtedly  the  Cephalopoda  are  the  best  guides  in  cor¬ 
relating  strata  of  Mesozoic  age,  and  the  Authors  claim  that  eight 
