WHICH  HAVE  CONSOLIDATED  ON  STEEP  SLOPES. 
713 
whole  of  these  stony  beds  (A  2,  3,  4)  are  divided  by  joints  nearly  at  right  angles  to 
the  planes  of  bedding.  The  passage  from  the  upper  crust  or  scoriae  to  the  compact 
Eig.  2. — Section  of  lava  inclined  at  23°  and  29°  at  the  Bastione  del  Tocco  on  the  Scalazza  of  Aci  Beale. 
c,  d.  Section  running  east  and  west. 
d,  e.  Section  running  from  south  to  north,  or  at  right  angles  to  the  dip. 
A.  Uppermost  lava-current 1,  scoriaceous  crust ; 2,  3,  4,  compact,  stony  beds ; 5,  lower  scoriae. 
B.  Eed  or  burnt  surface  of  subjacent  tuff. 
dolerite  (A  2)  is  very  abrupt,  as  is  that  from  the  lower  part  of  the  stony  lava  (A  4),  where 
it  becomes  cellular  to  A 5,  or  the  underlying  scoriae.  This  last  is  about  2 feet  thick, 
and  consists  of  small  fragments  for  the  most  part  agglutinated  together.  At  its  con- 
tact with  the  uneven  surface  of  the  subjacent  tuff  (B)  it  fits  into  and  fills  up  the  depres- 
sions several  inches  deep  in  that  tuff,  which  is  composed  at  the  top  of  sand  and  lapilli 
burnt  red  for  a depth  of  from  1 to  2 feet.  Below  this,  but  not  visible  at  the  point  of 
section  (fig.  2),  is  a coherent  earthy  tuff  of  fine-grained  materials  and  a light  brown 
colour,  without  lapilli,  and  divided  somewhat  regularly  by  joints,  so  as  to  have  a columnar 
appearance. 
[This  fine-grained  stratum  rests  on  loose  volcanic  sand  of  a black  colour,  containing 
many  heavy  blocks  of  lava,  more  or  less  rounded,  such  as  are  seen  in  the  beds  of 
torrents  which  descend  from  the  flanks  of  Etna.  At  the  time  of  my  second  visit  to  Aci 
(1858),  several  of  these  hard  blocks,  from  12  to  16  inches  in  diameter,  had  just  been 
dug  out  of  the  black  sand  in  a vineyard  adjoining  the  Bastione.  The  whole  deposit, 
including  the  tufi",  resembles  the  transported  materials  observable  in  the  wide  water- 
courses which  furrow  the  western  slopes  and  base  of  Etna.  Below  the  above-mentioned 
tuff  and  loose  sand  is  seen  another  current  of  lava  40  feet  thick,  also  having  red  or  burnt 
tuff  below  it,  and  below  that  again  there  appear,  in  the  face  of  the  cliff  on  the  left  hand 
as  we  descend  the  Scalazza,  a series  of  other  beds,  among  which  are  four  lavas,  each 
reposing  on  red  and  altered  tuffs  or  soils.] 
To  return  to  the  inclined  dolerite  of  the  Bastione : we  have  first  to  consider  whether 
it  can  possibly  have  acquired  its  present  dip,  averaging  about  26°,  in  consequence  of  a 
landslip  or  any  other  movement  posterior  to  its  original  congelation.  That  it  has  not 
done  so,  is  demonstrated  by  the  fact  that  it  is  a continuous  part  of  an  unbroken  and  unin- 
terrupted lava-current,  the  uppermost  part  of  which  can  be  traced  for  several  hundred 
5 a2 
