144 
PROCEEDINGS  OF  THE  GEOLOGICAL  SOCIETY.  [May  1893, 
in  boilers.  Mr.  Reid  said  that  at  the  last  meeting  he  was  challenged 
to  produce  artificial  calcareous  tubes  with  definite  walls,  the  only 
structure  visible  in  most  of  the  so-called  Girvanella.  The  apparatus 
illustrated  the  singular  effect  produced  by  fibres  in  causing  the 
deposition  of  carbonate  of  lime.  If,  instead  of  on  flat  hemp-fibres, 
the  incrustation  were  to  take  place  outside  Confervce  or  other  algae, 
the  result  would  be  a  knotted  mass  of  cylindrical  calcareous  tubes, 
like  those  found  so  abundantly  in  limestones  of  freshwater  as  well 
as  of  marine  origin. 
Prof.  T.  Rupert  Jones  remarked  that  analogies  are  of  very 
different  values.  In  this  case  large  vermiform  concretions  occur  on 
the  outside  of  fibres,  while  in  Girvanella  the  minute  body  itself  is 
composed  of  vermiform  tubules. 
The  following  communications  were  read  : — 
1.  “  On  the  Occurrence  of  Boulders  and  Pebbles  from  the  Glacial 
Drift  in  Gravels  south  of  the  Thames.”  By  Horace  W.  Monckton, 
Esq.,  E.L.S.,  E.G.S. 
2.  “  On  the  Plateau-Gravel  south  of  Reading.”  By  0.  A.  Shrub- 
sole,  Esq.,  E.G.S. 
3.  44  A  Eossiliferous  Pleistocene  Deposit  at  Stone,  on  the  Hamp¬ 
shire  Coast.”  By  Clement  Reid,  Esq.,  E.L.S.,  F.G.S.  (Communicated 
by  permission  of  the  Director-General  of  the  Geological  Survey.) 
The  following  specimens  were  exhibited  : — 
Specimens  and  microscopic  sections,  exhibited  by  Horace  W. 
Monckton,  Esq.,  E.L.S.,  F.G.S.,  in  illustration  of  his  paper. 
Specimens  exhibited  by  0.  A.  Shrubsole,  Esq.,  E.G.S.,  in  illus¬ 
tration  of  his  paper. 
Specimens  from  a  Pleistocene  Deposit  at  Stone,  on  the  Hampshire 
Coast,  exhibited  by  Clement  Reid,  Esq.,  F.L.S.,  F.G.S.,  in  illus¬ 
tration  of  his  paper. 
Specimens  from  Norcot-Kiln,  Tilehurst,  west  of  Reading,  exhibited 
by  J.  H.  Blake,  Esq.,  E.G.S. 
Specimens  of  inorganic  incrustations  and  Calcareous  Algae  to 
illustrate  the  structure  of  Girvanella ,  exhibited  by  Clement  Reid, 
Esq.,  E.L.S.,  F.G.S. 
Deposit  of  Lime  from  a  Kettle,  exhibited  by  W.  Topley,  Esq., 
E.R.S.,  E.G.S. 
Hew  sheets  of  the  Geological  Survey  Map  of  Sutherland*  exhL 
bited  by  Sir  Archibald  Geikie,  D.Sc.,  Eor.Sec.R.S.,  Y.P.G.S. 
