Yol.  49-] 
CLAYS  OF  THE  MALTESE  ISLANDS. 
125 
but,  considering  the  nature  of  the  clay  of  which  they  are  composed 
and  the  contained  foraminifera,  it  is  more  probable  that  many  of 
them  at  any  rate  are  indigenous  to  the  formation  in  which  they  are 
found,  and  that  they  owe  their  origin  to  concretionary  action  due  to 
the  mutual  attraction  of  the  clay-particles  one  for  the  other.  In 
connexion  with  this  point  it  is  important  to  note  that  the  chemical 
composition  and  the  mineralogical  constitution,  as  well  as  the  fossil 
contents  of  the  nodules,  are  similar  in  every  respect  to  that  of  the 
Clay  in  which  the  nodules  occur. 
According  to  the  chemical  analyses  made  by  Dr.  John  Murray, 1 
the  different  bands  of  the  Clay  vary  greatly  in  their  composition. 
These  analyses  I  have  repeated,  and  from  them  it  is  demonstrable 
that  the  proportion  of  calcium  carbonate  in  the  yellow  and  the  dark 
blue  clays  ranges  from  6  to  10  per  cent.,  in  the  light  blue  varieties 
from  22  to  40  per  cent.,  and  in  those  parts  where  the  Clays  graduate 
into  the  underlying  Globigerina- limestone  as  much  as  67  per  cent, 
of  calcium  carbonate  has  been  detected.  This  carbonate  is  made 
up  for  the  most  part  of  the  tests  of  foraminifera  and  the  discs  of 
coccoliths,  coccospheres,  and  rhabdoliths. 
Small  quantities  of  phosphoric  acid  and  traces  of  magnesia  were 
also  found  by  Dr.  Murray  in  several  specimens  of  Clay  from  Gozo. 
The  magnesia  is  more  distinctly  perceptible  in  the  rock  of  the  upper 
horizon  immediately  beneath  the  Greensands,  a  fact  which  I  am 
inclined  to  think  may  be  due  to  the  decomposition  of  glauconite 
(silicate  of  iron  and  magnesia),  a  mineral  which  occurs  very  plenti¬ 
fully  in  the  Greensands. 
The  following  table  shows  the  extent  of  the  quantitative  varia¬ 
tions  of  the  several  components  of  the  rock  : — 
Carbonate  of  lime  .  2  to  67  per  cent; 
Sulphate  of  lime  .  4  to  30  „ 
Carbonate  of  magnesia  .  faint  traces  to  distinct  traces. 
Phosphate  of  lime  .  traces  to  2  per  cent. 
Alumina  . . .  25  to  58  per  cent. 
Oxides  of  iron  .  4  to  10  „ 
Residue  insoluble  in  dilute  hydrochloric  acid  3  to  10  „ 
The  uppermost  Clays  are  very  compact  and  impermeable :  they 
therefore  form  the  water-bearing  stratum  of  the  Islands. 
IY.  The  Organic  Remains. 
Organic  remains  are  well  represented  in  the  Clays,  both  generically 
and  specifically,  but  they  are  not  equally  abundant  in  every  part 
of  that  formation.  Prof.  Leith  Adams,2  alluding  to  this  subject, 
expressed  an  opinion  that  the  fossils  in  the  Clays  are  as  numerous 
as  those  in  the  overlying  and  underlying  rocks ;  but  with  this  con¬ 
clusion  I  cannot  agree,  for,  despite  the  large  number  of  genera  and 
species,  the  number  of  individuals  falls  far  short  of  that  contained 
in  any  other  of  the  Maltese  formations. 
1  ‘The  Maltese  Islands,  etc.,’  Scot.  Geogr.  Mag.  vol.  vi.  (1890)  p.  449. 
2  Quart.  Journ.  Geol.  Soe.  vol.  xxxv.  (1879)  p.  519  et  seq. 
