﻿WEIGHT 
  AND 
  ADAMS 
  MALTESE 
  ECHINODEEMS. 
  473 
  

  

  will 
  be 
  found 
  that 
  what 
  appears 
  to 
  be 
  a 
  pale 
  bluish-white 
  sandstone 
  

   externally 
  is 
  a 
  dark 
  drab-coloured 
  rock 
  when 
  broken 
  up. 
  This 
  is 
  

   the 
  only 
  variety 
  I 
  can 
  safely 
  say 
  occupies 
  a 
  certain 
  position 
  ; 
  it 
  

   invariably 
  occupies 
  a 
  central 
  position 
  in 
  the 
  group 
  — 
  at 
  least 
  it 
  never 
  

   forms 
  the 
  uppermost 
  or 
  lowermost 
  stratum. 
  It 
  is 
  very 
  liable 
  to 
  

   exfoliate 
  on 
  exposure, 
  breaking 
  up 
  with 
  a 
  cleavage. 
  The 
  great 
  

   indent 
  in 
  the 
  east 
  coast 
  at 
  Marsa 
  Scirocco 
  has 
  been 
  formed 
  in 
  this 
  

   perishable 
  variety. 
  

  

  Hard 
  lumps 
  of 
  limestone 
  and 
  nodules 
  of 
  chert 
  are 
  often 
  inter- 
  

   spersed 
  thoughout 
  the 
  Calcareous 
  Sandstone; 
  the 
  latter 
  are 
  not 
  

   affected 
  by 
  strong 
  acids. 
  The 
  reddish-yellow 
  varieties 
  of 
  this 
  bed 
  

   owe 
  their 
  colour, 
  more 
  or 
  less, 
  to 
  the 
  presence 
  of 
  oxide 
  of 
  iron, 
  which 
  

   exists 
  in 
  much 
  less 
  quantity 
  in 
  the 
  c?ra&-coloured 
  variety. 
  The 
  

   nodular 
  beds 
  are 
  the 
  chief 
  objects 
  of 
  attention 
  in 
  this 
  group 
  ; 
  they 
  

   traverse 
  the 
  rock 
  at 
  variable 
  depths, 
  and 
  differ 
  as 
  to 
  extent, 
  thick- 
  

   ness, 
  &c. 
  There 
  is 
  one 
  bed 
  in 
  particular 
  which, 
  for 
  its 
  constancy 
  and 
  

   abundance 
  of 
  organic 
  remains, 
  deserves 
  especial 
  notice 
  ; 
  I 
  refer 
  to 
  

   that 
  overlying 
  the 
  Lower 
  Limestone. 
  The 
  nodules 
  are 
  of 
  irregular 
  

   shape 
  and 
  consistence, 
  and 
  are 
  usually 
  found 
  cemented 
  together 
  or 
  

   dispersed 
  throughout 
  the 
  sandstone. 
  They 
  are 
  various 
  as 
  to 
  consist- 
  

   ence, 
  being 
  often 
  crystalline, 
  or 
  merely 
  a 
  liver-coloured 
  porous 
  sub- 
  

   stance, 
  showing 
  a 
  whitish 
  surface 
  when 
  fractured. 
  As 
  to 
  their 
  being 
  

   of 
  organic 
  origin, 
  there 
  does 
  not 
  appear 
  to 
  me 
  any 
  proof 
  at 
  present 
  : 
  

   several 
  nodules 
  contained 
  casts 
  of 
  Shells, 
  chiefly 
  small 
  univalves 
  ; 
  the 
  

   Sharks' 
  teeth 
  and 
  Cetacean 
  bones 
  which 
  are 
  common 
  in 
  the 
  nodular 
  

   beds, 
  are 
  often 
  very 
  much 
  worn, 
  as 
  if 
  they 
  had 
  been 
  rolled 
  ; 
  Rete- 
  

   pores 
  and 
  marine 
  parasitic 
  Plants 
  are 
  often 
  found 
  in 
  the 
  nodules. 
  

   According 
  to 
  Capt. 
  Spratt's 
  description, 
  it 
  would 
  appear 
  that 
  there 
  

   is 
  only 
  one 
  bed 
  of 
  nodules 
  ; 
  but 
  this 
  is 
  incorrect, 
  as 
  in 
  cliff-sections 
  

   two 
  or 
  more 
  bands 
  may 
  often 
  be 
  observed. 
  As 
  to 
  the 
  position 
  of 
  

   these 
  nodular 
  seams 
  in 
  the 
  group, 
  they 
  occupy 
  diverse 
  levels, 
  some- 
  

   times 
  near 
  its 
  upper 
  limits, 
  and 
  often 
  lower 
  down. 
  It 
  does 
  not 
  

   appear 
  that 
  all 
  are 
  uniformly 
  distributed 
  throughout 
  the 
  sandstone 
  ; 
  

   the 
  one 
  stated 
  as 
  being 
  generally 
  present 
  at 
  the 
  junction 
  of 
  the 
  Cal- 
  

   careous 
  Sandstone 
  with 
  the 
  Lower 
  Limestone 
  is 
  most 
  regular 
  and 
  

   uniform. 
  

  

  5. 
  The 
  Lower 
  Limestone 
  is 
  often 
  compact, 
  hard, 
  and 
  semicrys- 
  

   talline 
  ; 
  oftener 
  a 
  coarse-grained 
  gritty 
  mass 
  composed 
  of 
  small 
  

   particles 
  of 
  Shells, 
  Corals, 
  and 
  Corallines. 
  A 
  curious 
  variety 
  shows 
  

   spheroidal 
  structures 
  like 
  travertine, 
  presenting 
  globular- 
  shaped 
  

   nodules 
  interspersed 
  in 
  an 
  irregular 
  and 
  varied 
  manner 
  through- 
  

   out 
  a 
  soft 
  rock. 
  This 
  variety 
  is 
  remarkable 
  in 
  being 
  apparently 
  

   devoid 
  of 
  fossils. 
  It 
  forms 
  large 
  portions 
  of 
  the 
  upper 
  strata; 
  

   all 
  these 
  vary 
  in 
  colour 
  from 
  yellowish 
  white 
  to 
  white. 
  The 
  

   harder 
  varieties 
  form 
  excellent 
  building- 
  stone, 
  but 
  do 
  not 
  take 
  

   so 
  fine 
  a 
  polish 
  as 
  the 
  " 
  Gozo 
  marble." 
  The 
  transition 
  between 
  this 
  

   rock 
  and 
  the 
  Calcareous 
  Sandstone 
  is 
  often 
  marked 
  by 
  the 
  nodular 
  

   bed 
  already 
  mentioned 
  and 
  an 
  abundance 
  of 
  interesting 
  fossils. 
  

   The 
  Scuiella 
  subrotunda 
  may 
  be 
  said 
  to 
  be 
  characteristic 
  of 
  the 
  Lower 
  

   Limestone 
  and 
  the 
  transition 
  between 
  it 
  and 
  the 
  group 
  above 
  ; 
  there 
  

  

  