WHICH  HA^"E  CONSOLIDATED  ON  STEEP  SLOPES. 
761 
a very  considerable  number  of  cones  do,  as  he  observes,  run  in  the  zone  first  alluded  to, 
namely,  from  Monte  Trigona  to  Monte  Egitto ; but  the  other  parallel  zone  from  Cubania 
to  Spagnuolo  is  so  short  and  comparatively  unimportant,  that  we  might  draw  another 
exactly  at  right  angles  to  it  {e.  g.  from  Monte  Peluso,  S.E.  of  Bronte  to  Monte  Santo, 
near  Linguagrossa),  which  would  comprehend  a zone  of  twice  the  length,  and  embracing 
at  least  double  the  number  of  points  of  lateral  eruption.  On  the  other  hand,  if  we  take 
the  summit  of  Etna  or  axis  of  Mongibello  as  a centre,  and  draw  a circle  round  it 
ha\dng  a radius  of  ten  geographical  miles,  we  find  that  nearly  all  the  lateral  cones,  200 
or  more  in  number,  all  carefully  laid  down  by  von  Waltebshausen,  are  embraced 
within  this  circular  area,  with  the  exception  of  a few  south  and  south-east  of  Nicolosi, 
and  one  or  two  others  in  the  north,  such  as  Monte  Santo  and  Mojo ; so  that  when  we 
speculate  on  the  causes  of  the  present  distribution  of  lateral  cones,  we  find  more  con- 
nexion between  them  and  the  position  of  the  great  central  focus,  than  with  any 
supposed  linear  clefts  running  N.W.  and  S.E. 
If,  again,  we  contemplate  the  Map  in  reference  to  the  spread  of  the  lavas  and  make 
a circle  round  the  same  great  axis,  with  a radius  of  about  twelve  geographical  miles,  we 
embrace  nearly  all  the  currents  which  ever  flowed  from  Etna,  whether  of  modem  or 
medieval,  or  older  date,  except  those  near  Catania  of  1669  and  1381. 
This  last  fact  may  help  to  bear  out  the  conclusion  stated  at  page  742,  that  the  pre- 
sent axis  of  Mongibello  may  be  as  old  or  older  than  that  of  Trifoglietto,  and  may  have 
always  been  the  chief  focus  of  eruption. 
(^[Becajpitulation  o/’Paet  II. 
The  following  are  the  principal  conclusions  which  I have  endeavoured  to  establish  in 
the  second  part  of  this  memoir. 
1st.  The  dip  of  the  ancient  beds  of  crystalline  and  fragmentary  matter  seen  in  the 
precipices  surrounding  the  Val  del  Bove,  are  not  such  as  to  support  the  theory  of  a 
linear  axis,  nor  of  a single  centre  of  upheaval  for  Mount  Etna. 
2ndly.  The  quaquaversal  dip  of  the  beds  first  observed  by  S.  von  Walteeshausen 
away  from  an  ancient  centre,  situated  three  miles  to  the  east  of  the  present  summit  of 
Etna,  together  with  the  horizontal  or  discordant  dips  of  other  superimposed  lavas  in  the 
precipices  at  the  head  of  the  Val  del  Bove,  imply  the  former  existence  of  at  least  two 
permanent  centres  of  eruption,  and  the  final  predominance  of  that  which  is  still  in 
actmty,  and  which  has  overwhelmed  the  smaller  or  more  eastern  cone. 
3rdly.  The  convergence  of  a large  number  of  dikes  towards  the  two  supposed  perma- 
nent centres  of  eruption  is  a fact  corroborative  of  the  theory  above  alluded  to. 
4thly.  If  such  be  the  structure  of  Etna,  and  such  the  conclusions  legitimately  dedu- 
cible  from  it,  we  must  abandon  the  elevation-crater  hypothesis ; for  although  one  cone 
of  eruption  may  envelope  and  bury  another  cone  of  eruption,  it  is  impossible  for  a cone 
of  upheaval  to  mantle  round  and  overwhelm  another  cone  of  upheaval  so  as  to  reduce 
the  whole  mass  to  one  conical  mountain. 
6 G 2 
