WHICH  HAVE  CONSOLIDATED  ON  STEEP  SLOPES. 
711 
tion  of  the  masses  once  submerged,  we  have  in  this  instance  to  allow  for  the  contempo- 
raneous building  up  above  the  waters  of  a great  volcano  thousands  of  feet  high,  as  also 
for  the  flowing  down  from  it  of  lava-currents,  some  of  them  partially  or  entirely  mask- 
ing the  old  inland  cliffs,  or  having  reached  the  coast  so  as  to  convert  tracts  of  sea  into 
land.  The  deltas,  moreover,  of  torrents  which  have  derived  nearly  all  their  sand, 
pebbles,  and  transported  blocks  from  the  volcanic  formations  of  various  dates,  have  in 
then’  turn  been  uplifted,  so  that  the  alluvial  accumulations  before  alluded  to  of  com- 
paratively modern  date,  now  constitute  terraces  terminating  in  low  inland  cliffs.  It  is 
necessary,  therefore,  to  bear  in  mind  all  these  and  other  peculiarities  in  the  physical 
geography  of  this  region,  before  we  can  understand  the  position  of  some  of  the  lavas 
about  to  be  described.]© 
Highly  inclined  stony  lava  of  Ad  Beale. 
The  town  of  Aci  Eeale*,  situated  about  twelve  miles  north  of  Catania  (see  Map, 
Plate  XLIX.),  stands  on  the  top  of  a clifi’,  in  which  a platform,  elevated  at  some  points 
near  the  town,  more  than  650  feet  above  the  sea,  ends  abruptly.  The  slope  of  the 
inclined  plane  forming  the  summit  of  this  platform  is  usually  at  an  angle  of  three  or 
four  degrees,  but  is  occasionally  steeper,  and  is  prolonged  two  or  three  miles  inland. 
The  precipice  between  the  town  and  the  sea  is  in  many  parts  perpendicular,  although  a 
line  dravm  from  the  top  to  the  bottom  would  rarely  exceed  45°,  and  in  some  parts  would 
only  amount  to  35°.  In  the  face  of  the  cliff  are  exposed  the  truncated  edges  of  those 
seven  lava-cm'rents  which  were  noticed  by  the  Canon  Recupero  in  his  ‘ Storia  Natu- 
rale  dell’  Etna,’  and  to  which  the  traveller  Brtdone  called  attention  in  England,  by 
stating  in  one  of  his  ‘ Letters  on  the  two  Sicilies,’  that  Recupero  had  been  able  by  the 
aid  of  these  lavas,  “ to  assign  a higher  antiquity  to  Mount  Etna  than  had  heretofore 
been  ascribed  to  our  planet  itself.”  Dr.  Carlo  Gemmellaro  assures  me  that  he  has 
verified  the  accuracy  of  the  Canon’s  descriptions,  especially  the  fact,  that  at  no  less  than 
seven  different  levels  there  intervene,  between  successive  currents  of  lava,  red  layers 
either  of  burnt  tuff  or  of  decomposed  scoriaceous  crusts  of  lava-currents,  which  have 
been  baked  and  reddened  by  heat,  or  as  Professor  Bunsen  would  say,  by  “ fnmerolic 
action”  superinduced  by  the  incumbent  lava.  Five  of  these  brick-red  bands  I saw 
myself  in  one  vertical  section  at  the  Scalazza,  a spot  of  which  I shall  presently  have 
more  to  say.  They  reminded  me  precisely  of  the  red  clays  and  tuffs  which  abound 
in  the  Island  of  Madeira,  where  many  subaerial  lavas  have  overflowed  the  surface  in 
succession,  and  where  there  have  been  sufficient  intervals  of  time  between  successive 
eruptions  for  the  decomposition  into  clay  of  the  crust  of  each  preexisting  lava,  or  where 
volcanic  sand  has  been  showered  down  from  above  or  washed  over  the  older  lava  by 
torrents  and  floods. 
We  need  not,  however,  seek  illustrations  of  such  a phenomenon  in  distant  regions, 
since  in  the  suburbs  of  the  neighbouring  Catania  similar  baked  and  altered  soils  of  a 
* When  I first  examined  the  clifi’s  of  Aci  Eeale  (October  1857),  I was  accompanied  by  a skilful  young 
geologist,  Signor  G-aetaxo  Gioegio  Gemmellaeo. 
MDCCCLVIII.  5 A 
