130  PROCEEDINGS  OF  TEE  GEOLOGICAL  SOCIETY.  [May  1893, 
Reverting  to  a  more  practical  view  of  the  case,  it  must  be  ad¬ 
mitted  that  previous  to  the  appearance  of  the  papers  by  Mr.  Mitchell 
and  Mr.  Buckman  our  knowledge  of  these  boundary-beds  was  to  a 
certain  extent  defective.  This  did  not  arise  from  want  of  discussion 
in  former  days ;  for  the  correlation  of  the  Dorsetshire  and  Glou¬ 
cestershire  beds  had  been  attempted  so  frequently  that  the  subject 
became  somewhat  distasteful,  and  men  shuddered  at  the  very 
mention  of  certain  Ammonite-zones.  Indeed  this  controversy 
extended,  at  one  time,  to  the  greater  part  of  the  Inferior  Oolite. 
However,  the  question  before  us  just  now  is  the  most  suitable 
boundary  between  the  Lias  and  the  Oolite. 
In  the  International  Geological  Map  of  Europe  the  base  of  the 
ojpalinus- zone  was  adopted  as  the  lower  boundary  of  the  Middle 
Jurassic.  To  a  certain  extent  this  is  a  conventional,  arbitrary  limit, 
though  not  without  many  natural  advantages  even  in  those  districts 
where  the  sequence  is  complete.  If  this  line  were  rigidly  adopted 
in  England,  the  bulk  of  the  Yeovil  and  the  whole  of  the  Mid  ford 
and  Gloucestershire  Sands  would  fall  into  the  Lias.  Hence  all  three 
groups  of  Sands  possess  one  feature  in  common,  viz.  that  they  lie 
below  the  opalinus- zone,  though  the  Sands  in  Gloucestershire  descend 
to  much  lower  horizons  than  either  of  the  other  two,  or,  in  other 
words,  they  were  deposited  earlier.  It  would  save  trouble,  perhaps, 
if  the  line  adopted  by  the  International  Geological  Congress  were 
adhered  to  in  the  SAY.  of  England,  and  in  this  way  no  particular 
violence  would  be  done  to  the  lithology,  as  the  Sands  in  all  three 
districts  would  be  relegated  to  the  Lias.  Such  an  arrangement 
would  also  suit  very  well  on  the  Yorkshire  Coast,  since  the  lower 
part  of  the  Dogger  is  certainly  within  the  opcdinus- zone,  while  the 
Sands  that  carry  the  Dogger  are  characterized  by  Ammonites  of  the 
Bumortieria  and  eZispemsits-korizons.  This  would  be  placing  the 
Lias-line  somewhat  higher  than  it  was  carried  by  Tate  and  Blake. 
It  must  not  be  supposed  for  a  moment  that  I  am  advocating  the 
adoption  of  this  or  any  other  line ;  my  object  is  merely  to  show  its 
incidence  in  one  or  two  localities.  In  drawing  a  boundary, 
especially  on  a  map,  there  are  many  aspects  of  the  question  to  be 
regarded,  and  the  resultant  is  partly  the  outcome  of  economic,  partly 
of  philosophical  considerations.  Geological  surveyors  must  look  at 
both  sides  of  the  question,  while  less  responsible  geologists  are 
granted  a  freer  hand.  I  must  confess  that,  on  the  principle  of 
taking  all  I  could  get,  I  did  include  these  Sands  within  the  range  of 
my  Monograph  of  the  Inferior  Oolite  Gasteropoda,  though  merely 
