Yol.  49.]  ANNIVERSARY  ADDRESS  OE  THE  PRESIDENT.  141 
immediately  below  the  Drifts  of  the  country,  go  out  on  the  rise 
towards  the  north.  The  red  sandstones  of  the  Keuper,  which  are 
supposed  to  represent  the  Waterstones  of  the  Midlands,  etc.,  are 
about  800  feet  thick.  The  Red  Marls,  or  Saliferous  Series,  imme¬ 
diately  above  the  main  salt-bed,  range  from  170  feet  to  about  300 
feet  in  thickness,  and  there  is  a  curious  absence  of  the  salt-rock 
itself  in  the  very  middle  of  the  field.  Generally  speaking,  according 
to  Mr.  Tate,  the  main  salt-rock  is  sandwiched  between  two  beds  of 
anhydrite,  while  the  underlying  saliferous  marls,  with  anhydrite, 
etc.,  held  by  Mr.  Wilson  to  form  the  base  of  the  Keuper  in  this 
region,  are  usually  thin,  but  vary  much  in  this  respect. 
The  underground  Permian  rocks  are  still  more  variable,  especially 
as  regards  thickness  :  ranging  from  300  feet  at  Whitehouse,  which 
lies  beyond  the  salt  area  on  the  west  (Tate),  to  nearly  900  feet  at 
Seaton  Carew,  also  beyond  the  salt  district  on  the  north-east.  At 
the  latter  place  the  upper  portion  of  the  series  consists  of  magnesian 
limestones  with  blue  shales,  gypsum,  and  anhydrite,  preceded  by  a 
great  mass  consisting  principally  of  light  grey  limestones  (?  mag¬ 
nesian).  No  mention  is  made  throughout  this  great  thickness  of 
beds  of  the  yellow  sands  so  characteristic  of  the  base  of  the  Permian 
in  other  parts  of  Durham,  and  especially  conspicuous  at  Cullercoats, 
in  Northumberland. 
In  concluding  this  Address,  so  far  as  it  has  gone,  a  brief  retrospect 
may  not  be  out  of  place.  Owing  to  the  interest  which  attaches  to 
superficial  geology,  this  portion  of  the  subject  may  perhaps  be 
regarded  as  having  received  more  than  its  fair  share  of  attention. 
In  regard  to  that  most  obscure  of  all  subjects,  the  history  of  the 
drifts  in  the  non-glaciated  regions,  we  seem  able  to  record  some 
real  progress.  Much  remains  to  be  done  in  this  direction,  and 
possibly  some  day  an  effort  may  be  made  effectually  to  correlate 
the  great  upland  gravel-sheets  of  the  south-western  counties  with 
those  farther  towards  the  east.  Coming  nearer  home,  it  will  be 
impossible,  henceforth,  to  maintain  that  there  had  not  been  a 
considerable  amount  of  excavation  effected  in  the  Thames  basin 
before  the  Chalky  Boulder-clay  reached  that  area. 
But  it  is  in  the  more  obviously  glaciated  regions  of  England  and 
Wales  that  the  chief  interest  has  been  centred,  and  in  this  respect 
there  can  be  no 'doubt  that  a  young  and  vigorous  race  of  geologists  is 
inclined  to  attribute  principally  to  glacier  action  many  of  the  pheno¬ 
mena  which  have  hitherto  been  explained  in  other  ways.  The  picture 
of  the  Irish  Sea  filled  with  ice,  over  2000  feet  thick,  is  one  which 
the  older  geologists  may  perhaps  never  be  induced  to  contemplate. 
