746 
SIE  CHAELES  LTELL  OX  THE  STEUCTUEE  OF  LAVAS 
were  striving  to  repair  the  injury  done  to  the  symmetry  of  the  cone,  and  restore  to  the 
volcano  its  proper  and  normal  shape. 
That  the  cone  of  Mongibello  was  once  higher,  and  that,  like  a large  number  of  active 
volcanos,  its  summit  has  been  truncated,  appears  from  the  occurrence  at  the  height  of 
more  than  9000  feet  of  a convex  platform,  which,  according  to  S.  v.  Walteeshausex’s 
measurement,  is  4150  metres  in  its  longest,  or  S.E.  and  X.AV.,  and  3000  metres  in  its 
shortest  diameter. 
c§[The  annexed  outline  view  (fig.  17)  will  show  the  manner  in  which  the  modem  cone(fl) 
rises  from  near  the  western  margin  of  the  platform  (5,  c),  which  S.  vox  AYalteeshausex 
considers  as  the  remnant  of  a crater  named  by  him  the  “ Cratere  EUiptico”  nearly  filled 
up,  but  part  of  the  outer  wall  of  which  still  remains,  and  which  will  be  described  in 
the  sequel.  The  area  called  the  Piano  del  Lago,  situated  at  a lower  level  to  the  south 
of  the  highest  cone,  is  regarded  by  the  same  observer  as  marking  the  site  of  another 
distinct  centre  of  eruption,  or  filled-up  crater,  2600  metres  in  diameter;  but  I was 
unable  to  verify  this  opinion,  there  appearing  to  me  no  sections  sufficient  to  establish 
the  fact  of  a long-continued  series  of  eruptions  from  any  fixed  point,  other  than  the 
present  culminating  focus.  There  is,  however,  such  a tendency  in  volcanos  to  shift 
their  principal  points  of  discharge,  that  a geologist  cannot  object  to  such  an  h^i-pothesis, 
if  it  can  be  shown  that  we  can  thereby  best  explain  any  observed  phenomena ; and  it 
was  probably  owing  to  the  limited  period  of  my  visit,  that  I failed  to  obtain  proofs  of  two 
adjoining  craters  formed  by  paroxysmal  explosions  and  then  afterwards  filled  up  to  the 
lips  by  lava  and  scoriee. 
Fig.  18. — Swnmit  of  Etna  as  seen  from  the  south  or  the  eastern  suburbs  of  La  Motta. 
a.  Highest  cone  as  seen  from  La  Motta.  b,  c.  Margin  of  Piano  del  Lago.  M.  Montag-nuola. 
The  annexed  sketch  (fig.  18),  which  I made  of  the  outline  of  the  higher  region,  as 
seen  from  the  south  or  from  the  eastern  suburbs  of  La  Motta,  will  show  in  how  analo- 
gous a manner  the  modern  cone  rises  there  above  the  Piano  del  Lago. 
The  geologist  must  not  infer,  from  the  term  Piano,  that  there  is  really  any  extent  of 
level  ground  or  table-land  near  the  summit  of  Etna.  The  whole  area  surrounding  the 
cone  might  rather  be  compared  to  a flattened  dome,  from  which  rise  several  volcanic, 
hills  of  considerable  size,  such  as  that  of  the  Torre  del  Filosofo,  and  another  much  more 
lofty,  called  Monte  Frumento,  rising  due  south  of  the  Casa  Inglese.  These  have  the  ordi- 
nary external  characters  of  lateral  cones  produced  by  single  eruptions.] s 
[_EllipUcal  crater. — I regret  that  I was  unable  to  ■\dsit  what  is  still  extant  of  the  walls 
of  the  “ Cratere  EUiptico  ” of  S.  vox  Walteeshausex,  whicli  is  situated  north  and  north- 
