WHICH  HAVE  CONSOLIDATED  ON  STEEP  SLOPES. 
739 
of  Finocchio  and  Musara  near  the  middle  and  northern  side  of  the  Val  del  Bove,  and 
in  those  of  the  northern  escarpment,  the  dips  were  north-easterly,  and  I now  there- 
fore came  to  the  conclusion  that  there  must  have  been  an  ancient  centre  of  eruption 
Pig.  14. — Map  of  the  Val  del  Bove,  showing  the  dip  of  the  beds  away  from  the  axis  of  Trifoglietto . 
in  that  part  of  the  Val  del  Bove  called  the  Piano  di  Trifoglietto,  at  a point  about  half- 
way between  the  Serra  Giannicola  and  the  hill  of  Zoccolaro,  which  I proposed  to  my 
companion  to  call  the  axis  or  cone  of  Trifoglietto.  At  the  same  time  I sketched  out 
an  ideal  section  (see  fig.  15),  which  I afterwards  reduced  to  a true  scale,  by  aid  of  that 
given  by  M.  Abich  in  fig.  2,  pi.  9 of  his  ‘ Illustrative  Views  of  Vesuvius  and  Etna.’ 
I had  seen,  during  my  ascent  to  the  summit  of  Etna  in  1828,  that  the  beds  in  the 
Cistema,  more  than  3000  feet  above  the  base  of  the  Serra  Giannicola  and  near  the  edge 
of  the  elevated  platform  called  the  Piano  del  Lago,  have  a gentle  dip  of  about  6°  in  nearly 
an  opposite  direction.  I therefore  now  inferred  that  Etna  must  have  had  at  one  period 
a double  axis,  or  two  points  of  permanent  eruption,  like  some  of  the  great  volcanos  of 
Java  described  by  Junghuhn*,  and  that  there  may  have  been  a saddle  as  that  author 
terms  it,  or  as  I propose  to  call  it,  an  intercolline\  space  between  the  two  cones  (as 
* Some  of  these  Javanese  cones  are  nearly  comparable  in  size  to  Etna,  and  have  had  two  or  more  centres 
of  eruption.  One  in  particular  called  Gede  may  be  cited,  in  which  one  regular  cone,  sloping  on  some  of  its 
sides  at  an  angle  of  30°,  is  truncated  like  Etna  and  is  9326  feet  high ; while  the  other  twin  cone,  Pangge- 
rango,  somewhat  less  lofty,  has  suffered  much  waste,  being  cut  into  on  one  of  its  sides  by  a deep  valley  com- 
parable to  the  Val  del  Bove.  The  saddle  connecting  the  two  mountains  is  7870  feet  high. — Junghtjhn’s 
‘ Java,’  vol.  i. 
f In  volcanic  regions  of  subaerial  origin  there  are  valleys  not  formed  by  aqueous  erosion,  nor  by  sub- 
sidence, nor  by  anticlinal  or  synclinal  flexures,  but  simply  by  the  budding  up  on  two  or  more  aides  of  vol- 
canic hdls  or  chains  of  hdls.  Mr.  Haetukg  and  I found  many  such  valleys  or  spaces  in  Madeira,  and  we 
found  it  very  convenient  to  have  a technical  term  for  them,  such  as  intercolline. 
