764 
SIE  CHAELES  LTELL  ON  THE  STEUCTUEE  OE  LAVAS 
the  Val  del  Bove,  are  conspicuous  beyond  the  rest  by  their  yolume,  and  by  being 
exclusively  composed  of  the  wreck  of  the  volcano  itself. 
The  coarsely  stratified  mass  before  alluded  to  (p.  709)  as  forming  the  terrace  on  which 
Giarre  stands,  would  be  called  “diluvium”  by  some  geologists,  and  much  resembles  the 
“ glacial  drift”  of  Northern  Europe  and  America;  yet  with  this  important  difference,  that 
none  of  the  blocks,  whether  rounded  or  angular,  have  as  yet  been  observed  to  exhibit 
polished  surfaces  with  rectilinear  striee  or  scratches  such  as  might  indicate  a glacial 
origin.  The  largest  angular  fragments  near  Giarre  are  occasionally  9 feet  in  diameter. 
The  blocks  are  of  trachyte,  basalt,  dolerite,  trachi-dolerite  or  grey  stone,  and  agglomerate ; 
in  short,  of  every  variety  of  rock  met  with  in  the  V al  del  Bove, — some  evidently  derived 
from  dikes. 
A great  torrent,  dry  for  a large  part  of  the  year,  which  passes  by  Giarre,  has  cut  a 
wide  channel  through  this  drift,  to  the  depth  of  more  than  40  feet,  without  reaching  the 
bottom ; and  near  Mangano,  about  four  miles  to  the  south,  there  is  a section  of  a similar 
alluvium,  60  feet  deep,  with  rounded  and  angular  blocks,  some  of  lai’ge  size,  occuiTing 
at  a higher  level,  and  overlying  the  Giarre  deposit,  making  the  thickness  at  that  place 
in  all  probability  more  than  150  feet. 
The  alluvial  region  (a,  Plate  XLIX.),  to  which  the  above-mentioned  di’ift  belongs, 
extends  ten  miles  from  north  to  south,  and  about  three  from  east  to  west.  It  has  been 
correctly  laid  down  by  S.  von  Walteeshausen  in  his  Map,  of  which  Plate  XLIX.  is  a 
reduced  copy.  The  lavas  fiowing  from  the  Val  del  Bove  have  covered  and  concealed 
from  our  view  a portion  of  its  western  limits,  as  we  may  infer  from  sections  seen  between 
Santa  Venerina  and  Santa  Leonardello,  in  the  banks  of  a torrent  which  fiows  down  ffom 
Zafarana.  But  the  northern  half  of  the  area  alluded  to  (a'  Map,  Plate  XLIX.),  which 
reaches  from  Giarre  to  the  Fiume  Freddo,  has  not  borrowed  its  materials  from  the  Val 
del  Bove,  but  must  have  derived  them  from  parts  of  the  mountain  immediately  north  of 
the  northern  escarpment  of  the  great  Caldera.  In  that  tract,  however,  the  thickness  of 
the  drift,  as  well  as  the  average  size  of  the  blocks,  is  visibly  less  than  in  a,  for  the 
transported  fragments,  as  before  stated,  are  most  voluminous  where  they  ought  to  be  so 
on  the  supposition  that  the  Val  del  Bove  was  their  source. 
\yalle  del  Tripodo,  and  proof s of  aqueous  erosion  anterior  to  the  Val  del  Bove. 
It  may  perhaps  be  suggested  that  the  deposit  of  Giarre  and  Mangano  might  have 
been  swept  down  by  rivers  from  the  old  cone  when  it  was  still  entfre  and  before  the 
Caldera  originated,  in  favour  of  which  theory  it  might  be  urged  that  in  the  Val  del 
Bove  at  present  we  discover  no  action  of  running  water  capable  of  causing  extensive 
denudation;  also  that  we  may  well  imagine,  during  some  former  suspension  of  erup- 
tions on  the  eastern  flank  of  the  volcano,  that  rawnes  like  the  Ca^  a Grande  may  have 
been  gradually  excavated  in  the  wide  space  separatmg  the  two  hills  of  Calanna  and  of 
Caliato. 
In  order  to  test  the  value  of  such  an  hypothesis,  I determined  to  explore,  from  their 
