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ME.  S.  S.  BTJCKMAN  ON  THE  BAJOCIAH 
[Nov.  1893, 
horizons,  and  their  rapidity  in  development  makes  them  peculiarly 
suitable.  Therefore,  as  far  as  possible,  the  chronological  unit  and 
the  Ammonite-species  should  go  together;  and  any  system  of 
grouping  the  chronological  units  should  depend  on  the  epacme, 
acme,  and  paracme  of  Ammonite-families.  No  doubt,  in  practical 
application,  the  epacme  of  one  family  would  be  found ^  contempo¬ 
raneous  with  the  paracme  of  another,  so  that  possibly  it  might  be 
necessary  to  consider  only  two  of  the  developmental  phases. 
Such  terms  as  Bajocian,  Toarcian,  etc.,  might  be  used  from  the 
chronological  point  of  view  only,  to  express  the  successive  portions 
of  time  of  which  the  developmental  phases  of  Ammonite-families 
gave  evidence.  They  could  be  used  for  palaeontological  purposes,  and 
only  indirectly  would  have  reference  to  such  strata  as  might  have 
been  deposited  during  the  times  they  represent.  The  details  of 
this  scheme  cannot  be  discussed  now.  At  present  I  use  the  term 
(  Bajocian ’  simply  because  it  is  the  most  exactly  descriptive  term 
we  possess  for  the  strata  intended.  In  a  former  paper  laid  before 
the  Society,  I  advocated  a  particular  use  of  the  term  ‘  Toarcian.’ 1  .  In 
the  present  paper  the  Bajocian  will  commence  where  the  Toarcian, 
as  then  defined,  finished. 
The  Limits  of  the  District. — For  the  purpose  of  this  paper  I  define 
the  Sherborne  district  as  follows A  straight  line  from  Stoford  to 
Milborne  AVick,  a  distance  of  about  7 ^  miles  in  a  north-easterly 
direction,  enters  the  border  of  Dorset  a  few  yards  from  its  starting- 
point  at  Stoford  Quarry,  and  travels  for  some  six  miles  before  it 
leaves  Dorset  for  Somerset.  The  exposures  of  Bajocian  in  the 
Sherborne  district  are  to  be  found  not  far  from  this  line.  For 
rather  more  than  the  first  four  miles — the  Bradford  area- — the  strata 
are  thinly  and  but  partially  represented  ;  only  in  the  neighbourhood 
of  the  eastern  part  of  the  line — the  Sherborne  area — is  there  any¬ 
thing  like  a  regular  sequence. 
The  lower  part  of  the  Bajocian  of  this  portion  of  the  district  was 
most  imperfectly  known,  and  has  never  been  described.  That  a 
certain  quarry  near  Sherborne — Sandford  Lane  (Combe) — yielded 
an  Ammonite-fauna  differing  from  anything  else  in  the  district  was 
an  acknowledged  fact ;  but,  as  the  quarry  had  not  been  worked  for 
some  sixteen  years,  complete  ignorance  prevailed  concerning  the 
relationship  of  its  strata  to  superjacent  and  subjacent  deposits. 
In  order  to  clear  up  this  mystery,  Mr.  Hudleston  and  myself 
undertook,  in  the  summer  of  1892,  an  investigation,  during  which, 
with  the  kind  consent  of  the  landlord,  I.  K.  D.  Wingfield-Digby, 
Esq.,  M.P.,  we  opened,  on  our  own  account,  certain  long-closed 
quarries.  Our  thanks  are  due  to  Mr.  Digby,  his  agents  and  his 
tenants,  for  their  kind  assistance,  which  materially  contributed  to 
the  success  of  our  investigations. 
On  Zonal  Correlation.— The  geological  unit  for  the  correlation  of 
strata  has  hitherto  been  the  4  zone.’  Gradually,  however,  it  has 
been  felt  that  either  the  zones  must  be  increased  in  number,  or 
1  ‘  Cotteswold,  etc.,  Sands/  Quart.  Journ.  Geol.  Soc.  vol.  xlv.  (1889)  p.  440. 
