760 
SIE  CHAELES  LTELL  OX  THE  STEUCTrEE  OF  LAVAS 
dip  of  the  beds.  In  volcanos  in  general  the  frequent  association  of  highly  inclined 
lavas  and  of  numerous  dikes,  does  not  imply  that  the  injection  of  melted  matter  into 
fissures  has  tilted  the  beds,  but  that  near  the  principal  crater,  where  earthquakes  rend 
the  mountain  and  where  lava  is  ever  ready  to  flow  into  rents,  there  are  causes  at  work,  as 
already  stated  at  p.  751,  to  produce  a steep  slope  in  the  ejected  and  outpoured  matter. 
When  we  recede  four  or  five  miles  from  the  great  centres  of  eruption  on  Mount 
Etna,  still  continuing  within  the  domain  of  the  old  lavas,  as  in  the  valleys  of  Calanna. 
S.  Giacomo,  and  Cava  Secca,  we  find  very  few  dikes,  only  three  in  S.  Giacomo,  and  one 
in  Cava  Secca,  which  last  is  more  remote  from  the  centre  of  eruption ; at  the  same  time 
the  lavas  begin  to  dip  less  steeply,  and  to  form  a much  more  considerable  proportion  of 
the  whole  mass.  The  lavas,  indeed,  in  these  sections  are  sometimes  separated  only  by 
such  scoriae  as  may  have  formed  the  top  crust  of  an  older  and  the  base  of  a newer 
current,  or  occasionally  by  tuffs  chiefly  of  alluvial  origin. 
Lateral  cones  of  Etna. 
I was  surprised  at  finding  no  clear  indications  of  buried  lateral  cones  in  the  walls  of 
the  Val  del  Bove,  since  there  are  so  many  in  Madeira  at  great  depths,  some  of  them 
overwhelmed  by  an  accumulation  of  lavas  and  tuffs  more  than  1000  feet  in  thickness. 
Whether  some  of  the  uTegularities  of  stratification  and  dip  seen  in  the  great  escarpments 
and  in  outliers,  such  as  Finocchio  Inferiore,  accompanied  by  many  dikes,  may  be  con- 
nected with  ancient  points  of  local  eruption,  is  a fit  subject  for  future  investigation. 
The  evidence,  so  far  as  I was  able  to  inquire,  did  not  seem  to  me  satisfactory,  and  I 
therefore  infer  that,  at  the  period  when  the  two  permanent  centres  of  eruption  were 
active  (those  ofTrifoglietto  and  Mongibello),  whether  contemporaneously  or  in  succession, 
there  were  few  if  any  lateral  outbreaks.  The  great  phase  of  lateral  eruption  seems  to 
have  begun  about  the  time  when  the  truncation  of  Mongibello  and  the  gradual  formation 
of  the  Val  del  Bove  were  in  progress,  and  after  much  bodily  upheaval  of  Etna  and  the 
adjoining  country  had  been  gradually  brought  about. 
Baron  S.  von  Waltershausen  has  remarked*  that  there  are  certain  spaces  within  the 
volcanic  region  of  Etna,  where  lateral  cones  are  wanting,  or  nearly  so,  and  others  where 
they  abound.  Thus  he  observes  that  in  the  dhection  from  Paterno  to  Bronte,  from 
S.S.E.  to  N.N.W.,  and  again  from  Aci  Beale  towards  Linguagrossa,  from  N.  to  S.  (see 
Map,  Plate  XLIX.),  there  are  two  zones,  each  of  them  about  eight  miles  broad,  'without 
cones;  and  again,  there  are  two  zones  nearly  parallel  to  each  other,  running  fr'oni  S.E.  to 
N.W.,  where  lateral  cones  are  in  great  profusion,  the  first  from  Monte  Trigona  to  Monte 
Egitto,  and  the  second  from  M.  Cubania  to  M.  Spagnuolo ; and  these  dfrections  he  thinks 
have  some  relation  to  the  larger  axis  of  the  central  nucleus  of  Etna,  and  to  the  strilve  of 
a certain  set  of  dikes  which  do  not  radiate  from  the  centres,  whether  of  Trifoglietto  or 
Mongibello,  before  mentioned.  A glance  at  the  Map  which  accompanies  this  paper, 
reduced  by  permission  from  S.  von  Waltershausen’s  large  ‘Atlas,’  will  show  that 
* Atlas,  V.  and  VI.  p.  4. 
