748 
SIE  CHAELES  LTELL  ON  THE  STErCTHEE  OF  LAYAS 
filled,  and  possibly  some  centre  of  discharge,  bearing  to  the  actual  crater  the  same  kind 
of  relation  which  the  Chahorra  now  bears  to  the  Peak  of  Teneriffe. 
I found  on  the  summit  of  the  highest  cone,  when  I nsited  it,  September  21,  1858, 
two  craters,  one,  the  western,  much  smaller  than  the  other,  and  separated  by  a narrow 
wall  of  highly  inclined  beds  of  ejected  scoriae  from  the  chief  abyss,  implying  that  within 
this  limited  space  the  modern  eruptions  have  not  been  strictly  constant  to  one  focus. 
JuNGHUHN  infers,  from  his  experience  in  Java,  that  where  there  are  two  pennanent 
foci  of  eruption  in  the  same  mountain,  they  are  to  be  considered  as  a fragment  of  a chain 
of  volcanos.  If  a third  occurs,  as  sometimes  happens  in  one  and  the  same  Javanese 
group,  the  three  are  always  linearly  arranged.  In  like  manner,  S.  vox  WALTEKSHArsEX 
imagines  that  in  the  upper  part  of  Etna  (or  the  area  of  the  axis  of  Mongibello)  the  two 
ancient  centres,  before  alluded  to,  are  in  a line  running  N.  36°  48'  W.,  which,  if  pro- 
longed, would  strike  the  axis  of  Trifoglietto.  He  therefore  supposes  all  the  emptions 
of  these  three  foci  to  have  broken  out  along  one  great  fundamental  fissure  I was  un- 
able, as  before  stated,  p.  746,  to  find  sections  to  test  or  bear  out  these  generalizations.] 
By  reverting  tb  the  section  (fig.  16,  p.  743),  the  reader  will  see  that  the  great  northern 
escarpment  of  the  Val  del  Bove,  called  the  Concazze,  terminates  in  its  higher  or  western 
extremity  in  a precipice,  which  faces  the  present  active  cone  or  axis  of  Mongibello,  and 
consists  of  lavas  which  dip  steeply  away  from  that  axis.  When  this  elevated  portion  of 
the  Concazze  was  formed,  the  great  crater  of  eruption  may  perhaps  have  been  more  to 
the  north  than  now,  and  the  cone  was  probably  loftier  than  that  which  now  exists.  Be 
this  as  it  may,  we  cannot  account  for  the  present  shape  of  the  northern  and  southern 
escarpments  of  the  Val  del  Bove,  and  the  manner  in  which  they  slope  away  fi’om  the 
highest  cone,  without  assuming  that  before  the  Val  del  Bove  originated  there  was  but 
one  conical  mountain,  which  embraced  within  it  the  subordinate  and  buried  cone  of 
Trifoglietto.  By  this  hypothesis  alone  can  we  explain  the  superior  altitude  of  the  west- 
ern boundary  of  the  great  valley,  and  the  gradual  diminution  in  height  of  the  two  great 
escarpments  as  they  trend  eastward. 
The  reader  will  be  better  able  to  restore  in  imagination  the  former  outhne  of  the 
single  cone,  before  it  was  truncated  at  the  top,  and  before  it  was  indented  by  the  great 
valley  on  its  eastern  flank,  by  referring  to  plate  12  of  S.  Walteeshausex’s  ‘ Atlas,’ 
where  an  accurate  and  very  descriptive  Hew  is  given  of  the  eastern  slope  of  Etna, 
including  the  Val  del  Bove,  as  seen  from  the  Torre  d’Archirafi,  a point  south  of  Eiposto, 
on  the  sea-coast. 
Hypothesis  of  upheaval  hy  injection. 
I have  stated,  in  my  preliminary  remarks,  that  geologists,  who  take  for  granted  that 
lava  cannot  congeal  in  continuous  stony  layers  on  slopes  exceeding  five  or  six  degrees, 
must  unavoidably  embrace  the  conclusion  that  nine-tenths  of  the  strata  which  constitute 
the  nucleus  of  Etna,  and  not  a few  of  the  beds  which  overlie  that  nucleus  unconform- 
* Atlaa  von  Etna,  part  7.  p.  3. 
