TTHICH  lLi'\T:  CONSOLIDATED  ON  STEEP  SLOPES. 
707 
Zappini  and  Tripodo  above  mentioned,  as  far  as  the  margin  of  the  Val  del  Bove.  The 
origin  of  the  neighhouring  valley  of  Calanna  is  more  doubtful.  Although  its  head  is 
closed  in  by  a precipice  called  the  Salto  della  Giumenta  (fig.  10,  p.  730),  the  clifis  of  its 
southern  side  are  prolonged  in  the  upper  part  of  Monte  Zoccolaro,  so  as  to  join  on  to 
the  southern  escarpment  of  the  Val  del  Bove.  Perhaps  there  existed  originally  an 
upper  valley  of  Calanna  above  the  “ Salto,”  before  the  external  configuration  and 
drainage  of  the  old  cone  was  totally  altered  by  the  formation  of  the  Val  del  Bove. 
There  may  have  been  a fall  of  water,  as  there  have  been  in  modern  times  cascades  of 
lava  over  the  Salto,  and  such  a fall  may  have  hollowed  out  the  valley  by  cutting  its 
v.'ay  backward  as  far  as  the  precipice  or  Salto,  just  as  the  torrent  of  the  Cava  Grande 
is  now  causing  its  raVne  to  retrograde.  If  so,  we  may  admit  that  other  valleys  may  in 
like  manner  have  furrowed  the  eastern  slopes  of  the  ancient  cone  between  the  hills  of 
Calanna  and  Caliato,  before  the  origin  of  the  Val  del  Bove,  in  which  case  much  allu- 
vium would  no  doubt  have  been  swept  down  to  the  sea  or  to  its  borders  at  that  early 
epoch.  But  admitting  the  possibility  of  such  erosion  of  early  date,  I nevertheless  do  not 
hesitate  to  attribute  the  bulk  of  the  Giarre  alluvium  to  the  excavation  of  the  Caldera 
itself,  for  reasons  which  will  be  more  fully  explained  in  the  sequel.] 
Q[_Section  of  alliivium  and  basaltic  lam  between  Giarre  and  La  Macchia. 
In  order  fully  to  understand  the  question  last  alluded  to,  I must  describe  a natural 
section  of  the  rocks  laid  open  by  the  torrent  descending  from  La  Macchia  to  Giarre. 
This  I examined  in  company  with  Dr.  Meecukio  and  Signor  G.  G.  Gemmellaeo  in  1857, 
and  reVsited  it  in  1858.  We  observed  that  the  alluvium,  attaining  a thickness  of  40  feet 
in  the  vertical  banks  of  the  torrent  in  the  suburbs  of  Giarre  (see  above,  pp.  709,  710),  re- 
poses on  volcanic  tufis  thinly  stratified,  which  in  some  places  emerge  in  low  hillocks  abo'\'e 
the  level  of  the  allmial  terrace.  As  we  ascended  the  dry  bed  of  the  stream,  we  saw  first 
a cuiTent  of  lava  capping  the  allmium,  and  together  with  it  forming  the  cliff  of  the  right 
bank ; then  on  the  left,  higher  up,  a powerful  mass  of  basaltic  lava,  90  feet  thick,  in  great 
part  columnar,  resting  on  30  feet  of  tuff,  the  perpendicular  section  being  120  feet  high. 
The  subjacent  tuff,  at  its  junction  with  the  columnar  basalt,  is  burnt  red.  At  this  spot 
the  two  formations  are  not  separated  by  any  intervening  gravel,  but  further  up  on  the  right 
hank,  a bed  of  alluvium,  10  feet  deep,  with  many  romided  and  some  huge  angular  frag- 
ments, 9 feet  in  diameter,  is  seen  between  the  basaltic  lava  and  the  older  tuff.  From  a 
study  of  the  whole  section,  the  details  of  which,  if  given  here,  would  detain  us  too  long, 
it  appears  that  an  ancient  water-course,  having  the  same  general  direction  as  that  now 
passing  by  La  Macchia,  was  first  cut  deeply  in  stratified  volcanic  tuff.  This  channel, 
narrow  at  first  or  near  La  Macchia,  widened  as  it  approached  the  present  site  of  Giarre, 
where  it  spread  out  into  an  allimal  plain  or  delta.  A current  of  basaltic  lava  flowing- 
down  from  the  higher  region,  and  probably  from  the  Val  del  Bove,  then  filled  up  the 
old  channel,  accumulating  in  some  places  to  a depth  of  90  feet,  sometimes  resting 
directly  on  the  gravel-bed  of  the  torrent,  sometimes  immediately  on  the  tuff  which  rose 
MDCCCLVin.  5 H 
