730 
SIK  CHAELES  LTELL  OX  THE  STEECTUEE  OE  LAYAS 
undermining  of  the  ridge,  this  last  retained  its  full  height  mth  its  crest  or  “riggin” 
unimpaired  and  its  flank  even  steeper  than  before.  At  the  same  time  the  most  advanced 
portion  of  the  fluid  lava  was  stealing  on  beneath  a heap  of  scoriae  which  had  rolled  down 
from  the  front  or  lowest  extremity  of  the  ridge,  so  that  the  manner  in  which  the  fore- 
most part  grew  in  height  could  not  easily  be  seen. 
But  although  the  weight  or  hydrostatic  pressure  of  fresh  loads  of  melted  matter  piled 
upon  a current  not  yet  consolidated  may  rarely  if  ever  give  rise  to  lateral  ridges  in  the 
manner  first  suggested  at  p.  729,  it  may  nevertheless  and  doubtless  does  often  happen, 
that  this  same  pressure  acts  with  great  force  on  different  parts  of  the  sides  and  roof  of 
one  and  the  same  tunnel,  uplifting  a viscous  or  semi-fluid  mass,  and  remodelling  the  form 
of  the  whole  current.  ]» 
Inclined  lava  (^1852-53  at  the  Salto  della  Gimnenta,  or  head  of  the  Valley  of  Calanna. 
We  have  seen  that  in  the  course  of  the  eruption  of  1852  above  described,  the  lava 
descended  more  than  once  over  the  great  precipice,  above  400  feet  high,  called  the 
“ Salto  della  Giumenta,”  which  intervenes  between  the  hills  of  Calanna  and  Zoccolai-o 
(see  Map,  Plate  L.).  The  width  of  the  summit  of  this  decH\ity  is,  according  to  S.  vox 
Walteeshausen’s  Map,  about  200  English  feet,  but  the  space  over  which  the  lava  fell, 
according  to  a rough  estimate  which  I made  by  pacing  it,  is  considerably  less.  The 
annexed  drawing  will  give  a general  idea  of  the  appearance  of  the  dark  lava  encrusting  the 
Eig.  10. — Lava  ^1852  cascading  down  the  precipice  called  Salto  della  G-iumenta. 
steep  slope,  the  spots  faintly  shaded  with  vertical  lines  consisting  of  ancient  rocks,  chiefly 
composed  of  felspar  and  hornblende,  assuming  on  decomposition  a bro-\vn  ferruginous 
colour,  and  protruding  in  masses  with  almost  perpendicular  sides  like  the  rock  in  the 
middle  of  the  Falls  of  Schaifhausen,  or  like  Goat  Island  in  the  Falls  of  Niagara.  Some 
greyish  stripes  marked  a and  left  white  in  the  di’awing  represent  the  lava  of  1819,  which 
also  went  down  this  same  precipice,  but  which  has  been  since  for  the  most  part  covered 
