738 
SIR  CHARLES  LTELL  ON  THE  STRUCTURE  OF  LAVAS 
PART  II. 
ON  THE  STRUCTURE  AND  POSITION  OF  THE  OLDER  VOLCANIC  ROCKS  OF  MOUNT 
ETNA,  AS  SEEN  IN  THE  VAL  DEL  BOVE,  AND  ON  THE  PROOFS  OF  A DOUBLE 
AXIS  OF  ERUPTION. 
It  is  now  time  to  inquire  into  the  structure  of  what  has  been  called  the  nucleus  of 
Etna,  sections  of  which  are  seen  in  the  cliffs  which  wall  in  the  Val  del  Bove  on  three 
sides.  How  far  do  the  mineral  characters,  and  inclination  of  the  Tolcanic  masses  com- 
posing that  nucleus,  imply  that  they  were  erupted  from  one  or  more  central  craters,  and 
arranged  from  the  first  in  a conical  form ; or  how  far  can  it  be  maintained,  on  the  con- 
trary, that  they  were  originally  horizontal,  or  nearly  so,  and  were  then,  as  the  advocates 
of  the  Elevation-crater  hypothesis  contend,  brought  into  their  present  position  by  move- 
ments of  upheaval 
Proofs  of  a double  axis. — Cones  of  Trifoglietto  and  of  Mongihello. 
I was  aware,  from  my  examination  of  the  great  valley  on  the  eastern  fiank  of  Etna 
in  1828,  that  the  beds  seen  both  in  the  north  and  south  escai*pment  dip  away  from  the 
valley ; but  in  that  year  I had  not  time  to  satisfy  myself  in  what  direction  they  were 
inclined  in  the  lofty  western  escarpment,  at  the  upper  end  of  the- great  amphitheatre  and 
below  the  highest  part  of  Etna.  I had  observed,  as  Hoffmaxst  and  others  did  after  me, 
that  there  were  large  amorphous  rocks  at  the  foot  of  the  Serra  Giannicola  in  which  no 
stratification  is  discernible,  and  which  consist  in  great  part  of  innumerable  dikes,  some 
of  very  large  dimensions,  penetrating  tuffs  and  agglomerates,  the  latter  so  altered  by  the 
intrusive  matter,  that  the  only  divisional  planes  to  be  seen  are  such  as  are  parallel  to 
the  walls  of  the  dikes.  But  on  this  occasion  (October  1857),  I found  masses  of  con- 
siderable thickness,  not  far  above  the  base  of  the  Serra  Giannicola,  distinctly  stratified. 
The  rocks  alluded  to  consist  of  alternations  of  trachyte  and  trachytic  agglomerate  in  beds 
of  variable  thickness,  dipping  at  angles  of  from  20°  to  28°  to  the  north-west,  or  towards 
the  central  axis  of  Etna,  that  axis  being  about  three  miles  distant  in  a hoiizontal 
direction. 
My  companion.  Signor  G.  G.  Gemmellaeo,  had  become  well  acquainted  dm'ing  pre- 
■nous  visits  with  this  fact  of  a northerly  dip  in  the  Giannicola  beds,  which  was,  I believe, 
first  discovered  by  Baron  S.  von  Waltekshausen  ; for  I learnt  on  my  retm-n  to  England 
that  it  had  long  been  kno-wn  to  him,  although  not  as  yet  published  in  his  ‘Atlas,’  the 
fifth  and  sixth  Numbers  of  which  had  not  appeared  in  1857.  I was  the  more  struck  -with 
the  discovery,  from  having  on  the  same  day  observed  that  the  beds  in  the  lower  half  of 
Zoccolaro  (see  Map,  fig.  14),  which  are  directly  opposite,  or  about  two  miles  to  the  S.E., 
and  very  similar  in  colour  and  mineral  composition,  dip  in  a contrary  dii’ection,  or  to 
the  S.E.,  while  those  at  the  foot  of  the  Montagnuola,  as  well  as  those  between  it  and  the 
Giannicola,  are  inclined  to  the  S.W. 
I knew,  from  what  I had  seen  of  Etna  in  1828,  that  in  the  outlying  and  isolated  rocks 
