The  Doncaster  Earthquake  of  1905.  191 
epicentre  half  a  mile  north  of  Bawtry,  and  the  other  about  4  miles 
east  of  Crowle  and  close  to  the  centre  of  the  disturbed  area  of  the 
Hessle  earthquake  of  April  13th,  1902.  The  distance  between  the 
two  epicentres  is  about  17  miles.  The  disturbed  area  contains 
about  17,000  square  miles,  including  the  whole  of  the  counties  of 
Lincoln,  Nottingham,  Derby,  Stafford,  Leicester,  and  Kutland,  the 
greater  part  of  Yorkshire,  and  portions  of  Lancashire,  Cheshire, 
Shropshire,  Worcestershire,  Warwickshire,  Northamptonshire,  Cam- 
bridgeshire, and  Norfolk.  The  originating  fault  runs  from  about 
E.  38D  N.  to  W.  38 D  S.,  and  appears  to  be  nearly  vertical  within  the 
south-western  focus  and  inclined  to  the  south-east  in  the  north- 
eastern focus.  The  first  and  stronger  movement  took  place  within 
the  south-western  focus.  A  twin-earthquake  is  probably  due  to 
the  differential  growth  of  a  crust-fold  along  a  fault  which  intersects 
it  transversely,  the  first  movement  as  a  rule  being  one  of  rotation 
of  the  middle  limb,  accompanied  by  the  almost  simultaneous  slip  of 
the  two  arches,  and  followed  soon  afterwards  by  a  shift  of  the 
middle  limb.  The  movements,  in  which  the  Doncaster  earthquake 
originated,  presented  a  slight  variation  in  this  order.  They  con- 
sisted of  successive,  but  continuous,  displacements,  first  of  the 
south-western  arch,  then  of  the  middle  limb,  and  finally  of  the 
north-eastern  arch. 
December  6th.— J.  E.  Marr,  Sc.D.,  F.R.S.,  President, 
in  the  Chair. 
The  following  communications  were  read  : — 
1.  'The  Physical  History  of  the  Great  Pleistocene  Lake  of 
Portugal.'     By"  Prof.  Edward  Hull,  LL.D.,  F.R.S.,  F.G.S. 
The  formations  bordering  the  lower  banks  of  the  Tagus  near 
Lisbon  are  arranged  by  the  author  in  the  following  order  of 
succession: — 
0.  Recent  &  Quaternary.        Alluvia  of  the  Tagus. 
5.  Lacustrine.  I  f*v}s  wit^  LVm^  (Lacustre  superior). 
I  panels  and  gravel. 
4.  Post-Pliocene  &  f  Not  represented,  unless  by  some  land-glacial 
Pliocene.  [      beds  due  to  elevation. 
3.  Miocene.  '  Almada  Beds.'    Calcareous  marls  and  lime- 
stones; with  marine  fossils. 
2.  Eocene  ('?).  Unfossiliferous   sands   and   gravels   (Lacustre 
inferior). 
1.  Upper  Cretaceous.  Hippurite-Limestone. 
A  description  is  given  of  the  Lacustre  superior ;  the  Almada  Beds 
are  considered  to  be  Miocene,  and  as  the  Pliocene  is  not  represented, 
except  possibly  by  certain  glacial  deposits,  the  author  considers  that 
that  period  was  one  of  great   uplift,  when  the  suboceanic  gorge, 
