Yol.  49.] 
OF  THE  SHERBORNE  DISTRICT. 
521 
C.  That  the  change  in  the  generic  constitution  of  the  Ammonite- 
fauna  of  the  Witchcllice  sp.  hemera  compared  with  that  of  the 
concavi  hemera  is  a  most  remarkable  fact. 
D.  That  the  fact  of  this  change  warrants  a  chronologico-palseonto- 
logical  line  of  separation  either  before  or  after  the  discitce 
hemera. 
E.  That  if  the  fact  of  Sonninia  being  in  its  acme  in  the  discitce 
hemera  be  proved,  and  if  this  fact  be  considered  of  more 
chronological  importance  than  that  of  the  Hilcloceratidce  being 
in  their  paracme  at  the  same  time,  then  the  line  of  division 
will  be  drawn  before  the  discitce  hemera.  Otherwise  it  will  be 
drawn  after  it. 
P.  That,  in  the  former  case,  if  the  Bajocian  were  used  as  a  chrono¬ 
logical  term  to  coincide  with  the  acme  and  paracme  of  the 
Sonninince ,  it  would  comprise  the  hemerae  discitce ,  Witchellice , 
Sauzei ,  Humphriesiani , — and  an  age  of  hemerae  with  richer 
Ammonite-faunae  it  would  be  difficult  to  find  in  the  Jurassic 
period.— August  8th,  1893.] 
Discussion. 
The  President  said  that  the  absence  of  the  Author  was  much  to 
be  regretted,  as  the  paper  was  evidently  one  of  importance. 
Speaking  with  reference  to  the  so-called  Sowerbyi-zoiiQ,  he  said 
that  Mr.  Buckman  in  former  years  had  maintained  that  this  was 
represented  by  the  conrcivus- bed  of  Bradford  Abbas,  which  is  there 
the  principal  fossil-horizon.  He  now  recognized  it  in  his  'WitchelUa- 
beds,  which  also  contained  Sonninia  Sowerbyi,  and  there  was  little 
doubt  that  in  so  doing  he  was  on  the  right  track. 
He  (the  President)  supposed  that  the  Author  referred  .all  the 
deposits  he  was  describing  to  the  Bajocian.  If  so,  he  had  somewhat 
modified  his  views  on  this  point  also,  for  in  a  former  paper  he  had 
regarded  at  least  three  of  his  ‘  emata  ’  as  Toarcian. 
These  were  matters  of  detail,  but  a  still  more  important  question 
was  involved,  namely,  that  of  method.  We  were  no  doubt  coming 
to  a  crisis — he  might  almost  say  to  a  revolutionary  period — in  the 
history  of  geological  investigation.  He  remembered  the  time  when 
the  subdivision  of  the  Inferior  Oolite  into  three  zones  was  regarded 
as  involving  almost  unnecessary  detail ;  but  what  were  three  zones 
compared  wfith  twelve  ‘emata’?  Such  a  subdivision,  based  on 
changes  in  the  Ammonite-faunae,  could  onty  be  effected  by  one 
well  versed  in  the  morphology  of  the  group.  He  could  not  test  the 
accuracy  of  the  Author’s  work,  but  he  was  satisfied  that,  although 
something  like  three  zones  were  necessary  for  general  grouping, 
sub-zones  or  ‘emata’  were  useful  as  adjuncts,  and  he  consequently 
believed  that  the  Author  was  working  in  the  right  direction.  His 
own  work  on  the  Gasteropoda  had  led  him  to  recognize  that  special 
forms  were  limited  to  certain  horizons.  It  was  scarcely  too  much 
to  say  that  if  rocks  were  to  be  studied  in  this  minute  way  the  whole 
of  stratigraphical  palaeontology  -would  be  revolutionized. . 
