WHICH  TLAYE  CONSOLIDATED  ON  STEEP  SLOPES. 
765 
lower  to  their  upper  terminations,  the  two  principal  valleys  of  aqueous  erosion  which 
slope  upwards  from  the  foot  of  the  cone  to  the  southern  margin  of  the  Caldera. 
Fig.  23. — Furrows  of  aqiheous  erosion  on  thecone  of  Tengger  (from  Junghtthn’s  ‘Java,’  vol.  ii.  part  2,  p.  588). 
Those  who  are  conversant  with  Junghuhn’s  ‘Volcanos  of  Java,’  are  well  aware  of 
the  nature  and  value  of  this  test ; for  they  will  remember  that  the  flanks  of  volcanic 
cones  which  are  in  full  activity  are  free  from  furrows  eaten  out  by  running  water; 
whereas  such  as  have  been  long  extinct  or  are  in  a state  of  moderate  activity,  exhibit  a 
great  number  of  ratines,  from  300  to  600  feet  deep,  excavated  by  torrents,  and  parted 
fr’om  each  other  by  “ribs”  or  ridges  of  volcanic  rocks,  compared  by  Junghuhn  to  the 
spokes  of  an  umbrella.  All  these  furrows  grow  narrower  and  shallower  when  traced 
upwards,  and  come  to  an  end  before  they  reach  the  rim  of  the  crater,  as  at  a,  b,  in  the 
great  volcano  called  Tengger ; whereas  in  such  volcanic  cones  as  have  been  truncated 
by  explosions  and  subsidences,  after  considerable  aqueous  erosion,  the  rim  is  invariably 
indented,  as  would  be  the  case  if  the  line  c,  d represented  the  margin  of  such  a cavity. 
On  applying  this  test  to  Etna,  I found  that  the  crest  of  the  southern  escarpment  of  the 
Val  del  Bove,  between  the  Montagnuola  and  Zoccolaro,  was,  as  a general  rule,  very 
entire  and  unbroken,  but  that  there  were  notches  or  abrupt  depressions,  several  hundred 
feet  deep,  precisely  at  the  two  points  where  the  upper  ends  of  the  valleys  called  the  Val 
dei  Zappini  and  the  Valle  del  Tripodo  (see  Map,  Plate  L.)  joined  the  crest.  Hence  it 
is  natural  to  conclude  that  the  valleys  in  question  are  of  older  date  than  the  Val  del 
Bove,  and  that  their  higher  extremities  were  once  prolonged  towards  the  upper  region 
of  the  cone,  and  were  cut  ofif  when  the  Caldera  was  formed.  Such  an  explanation, 
however,  of  the  facts  would  be  fatal  to  any  theory  which  refers  to  a single  catastrophe, 
or  to  any  one  mode  of  operation,  whether  slow  or  sudden,  the  upheaval  of  Etna,  the 
tilting  of  the  inclined  beds,  and  the  opening  of  the  great  cavity  called  the  Val  del  Bove. 
The  dmding  “col”  which  parts  the  Valle  del  Tripodo,  the  largest  of  the  two  valleys 
above  mentioned,  from  the  Val  del  Bove,  deserves  the  attention  of  every  lover  of  the 
pictm'esque,  as  well  as  of  every  geologist,  though  my  guides  assured  me  that  in  their 
time  they  had  never  heard  of  its  having  been  visited  by  any  traveller.  It  may  be 
reached  from  Zafarana  without  fatigue  by  the  aid  of  mules  in  one  day,  returning  in  the 
evening.  On  one  side  of  the  narrow  ridge,  6000  or  7000  feet  above  the  sea,  we  look 
