76  PROCEEDINGS  OF  THE  GEOLOGICAL  SOCIETY.  [May  1 895. 
tion  occurs  at  lower  levels,  and  that  the  deposition  of  the  Plateau- 
gravels  covers  most  of  the  geological  time  represented  by  the 
Pliocene. 
Stimulated  by  the  example  of  Prof.  Prestwich,  Mr.  Monckton  has 
lately  studied  with  much  attention  the  gravels  on  the  south  side  of 
the  Thames  from  Guildford  to  Newbury.  He  concludes  that  the 
greater  part  of  the  hill-gravels  belongs  to  the  Southern  Drift  of 
Prestwich,  and  that  the  valley-gravels  mostly  consist  of  material 
derived  from  the  Southern  Drift.  Small  patches  of  what  he  identi¬ 
fies  as  Westleton  shingle  and  Glacial  gravel  occur  near  Heading 
and  Twyford.  He  divides  the  Southern  Drift  into  three  classes,  of 
which  the  oldest  is  probably  the  Tipper  Hale  type,  characterized  by 
the  abundance  of  small  quartz-pebbles  and  the  scarcity  of  chert. 
The  gravels  of  Chobham  Eidges  and  Silchester,  though  differing  as 
0  the  amount  of  quartz-pebbles  and  chert,  were  probably  nearly 
contemporaneous.  He  rejects  the  theory  of  marine  action. 
The  entire  subject  of  the  hill-  or  plateau-gravels  south  of  the 
Thames  is  indeed  full  of  difficulty,  but  there  does  seem  a  preponder¬ 
ance  of  opinion  in  favour  of  their  freshwater  origin,  including  ice 
to  a  certain  extent  in  that  category.  These  gravels  may  or  may  not 
have  been  continuous,  though  the  elongated  shape  of  many  of  the 
patches  is  thought  to  afford  an  indication,  in  some  cases,  of  fluvia- 
tile  origin.  Such  patches  are  certainly  answerable  for  many  of  the 
existing  hills  in  the  soft  Tertiary  districts  of  West  Surrey  and  East 
Perks.  Of  course,  as  the  valleys  were  excavated  or  deepened,  much 
of  the  gravelly  material  originally  on  the  plateau  would  remain  on 
the  flanks,  either  as  irregular  deposits  or  imperfect  terraces.  This 
is  an  almost  self-evident  proposition,  and  the  principal  question  for 
decision  relates  to  the  period  when  these  events  occurred. 
Some  answer  to  this  question  may  be  sought  in  another  paper  by 
the  indefatigable  Prof.  Prestwich  on  the  Drift  stages  of  the  Darent 
Valley,  where  he  observes  that  the  first  indent  of  that  valley  must 
have  been  subsequent  to  the  deposition  of  the  Lenham  Sands  (earliest 
Pliocene)  and  even  of  the  Eed  Clay-with-flints.  In  early  Pliocene 
times  a  plain  of  marine  denudation  was  shown  to  extend  over  the 
valley  of  Holmesdale,  and  in  pre-glacial  times  the  valley  was  scored 
by  streams  flowing  from  the  high,  central  Wealden  ranges.  The 
streams  centred  in  the  Darent  and  the  excavation  of  the  present 
valley  then  commenced.  The  Author  believes  there  is  a  gap  between 
the  pre-glacial  drifts  of  that  district  and  the  earliest  post-glacial 
drifts  of  the  valley,  a  gap  which  might  perhaps  be  covered  by  the 
epoch  of  extreme  glaciation.  The  paper  last  quoted  was  to  a  certain 
