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SIR  CHARLES  LTELL  OX  THE  STEECTURE  OF  LAVAS 
chio.  The  manner  in  which  detached  blocks  of  various  shapes  and  sizes  were  occasion- 
ally poised  one  upon  another,  on  very  narrow  ridges,  made  us  mar\-el  that  high  winds 
had  not  blown  them  dovm.  I chmbed  up  to  some  of  them,  to  ascertain  that  they  were 
not  soldered  on  to  the  mass  of  scorise  below ; but  I found  them  free  to  move,  and  only 
holding  on  by  the  slight  inequalities  of  their  surface.  At  no  point  could  I discover 
fissures  or  openings  in  the  scoriaceous  crust  out  of  which  melted  matter  might  ha’^  e 
escaped  in  a stream  so  as  to  fill  up  the  trough  below ; but  pieces  of  scorise  had  often 
rolled  down  in  great  numbers  into  the  troughs. 
At  length  gaining  Finocchio,  we  found  it  standing  like  a rocky  islet,  submerged  up  to 
its  middle  in  lavas  of  different  ages,  and  with  the  fresh  current  of  1852  near  its  base. 
The  rehef  afforded  to  the  eye  by  this  oasis  was  so  great,  that,  although  the  day  was 
cloudy,  the  green  turf,  enlivened  by  the  flowers  of  a yellow  ragwort,  looked  dazzling  by 
contrast  with  the  dark  surrounding  desert,  and  the  autumnal  crocus  {ColcMcum  autum- 
nale),  also  in  full  bloom,  seemed  more  than  ever  beautiful.  Retui’ning  to  the  spot  where 
we  had  left  our  mules,  we  at  length  rode  back  to  Zafarana,  over  another  part  of  the  new 
lava,  where  hundreds  of  fumeroles  rose  in  dense  white  columns  of  steam,  each  of  them 
quite  perpendicular,  for  there  was  not  a breath  of  wind ; and  conspicuous  from  having 
usually  a background  of  dark  lava  to  show  off  their  graceful  forms ; so  that  we  could  no 
longer  complain,  as  in  our  morning’s  ride,  of  the  featureless  monotony  of  the  scene. 
The  problem  ever  present  to  our  minds,  during  the  whole  of  this  excm’sion,  was  the 
cause  of  the  curvature  of  the  lava  into  a series  of  gigantic  wrinkles.  In  what  manner  ai'e 
we  to  accormt  for  these  longitudinal  and  nearly  parallel,  anticlinal  and  sjTiclinal  ridges  and 
troughs  1 It  is  well  known  that  every  stream  of  lava,  as  soon  as  its  sm’face  and  sides  have 
congealed,  is  encrusted  over  with  a covering  of  scorise  and  stony  fragments,  so  that  it 
may  be  said  to  run  in  a tunnel,  the  roof  of  which  is  in  most  cases  a flattened  arch.  The 
supply  of  liquid  from  the  source  or  vent  being  irregular  and  intermittent,  the  cm’rent 
now  and  then  halts  for  a while,  sometimes  for  hours,  days,  or  weeks,  during  which  time 
a solid  terminal  wall  is  often  produced,  and  one  stony  layer  after  another  may  then  be 
formed  gradually  within  the  outer  crust  by  the  lava  congealmg  on  the  sides  and  roof  of 
the  arched  tunnel.  Such  concentric,  internal  layers  ha^dng  consolidated  slowly  and  under 
pressure,  will  often  acquire  a compact  and  crystalline  texture.  But  when  fresh  supphes 
of  hot  lava  descend  from  the  source,  that  portion  of  the  current  which  still  remains  flmd 
or  viscous  being  reinforced,  may  burst  through  the  terminal  crust,  and  the  onward  pro- 
gress of  the  lava  recommences.  We  have  already  seen,  p.  724,  that  the  lava  of  November 
1852  was  actually  observed,  near  the  foot  of  the  Centenario,  to  flow  m an  arched  chan- 
nel, and  there  were  doubtless  many  other  similar  lava-ducts  haAing  a parallel  direction, 
or  running  longitudinally  in  reference  to  the  stream. 
c8[Mr.  ScEOPE  has  suggested  to  me,  that  Avhen  fresh  molten  matter  penetrates  into 
such  subterranean  ducts,  they  may,  by  hydrostatic  pressure,  cause  the  supermcumbent 
mass  to  crack  and  swell  up  into  steeper  arches  than  those  originally  produced ; and  I 
think  it  probable  that  such  may  be  the  true  explanation  of  tlie  phenomenon,  though 
