WHICH  HAVE  CONSOLIDATED  ON  STEEP  SLOPES. 
709 
After  reflecting  on  these  and  other  analogous  facts,  I was  desirous,  before  publishing 
in  detail  the  observations  which  Mr.  Hartung  and  I had  made  in  Madeira  and  the 
Canaries,  to  re^isit  Vesuvius  and  Etna,  which  I accomplished  in  the  autumn  of  1857. 
In  studying  Mount  Etna,  my  attention  was  principally  directed — 1st,  to  the  lithological 
character  of  those  modern  lavas  which  have  consolidated  on  steep  slopes ; and  2ndly,  to 
the  question  whether  any  proofs  can  be  found,  in  the  position  of  the  ancient  lavas  and 
tufls  of  the  great  volcano,  in  favour  of  the  doctrine  that  the  upheaving  rather  than  the 
eruptive  force  has  exerted  a dominant  influence.  I hope  at  no  distant  time  to  offer  to 
the  Society  the  results  of  my  observations  on  Vesuvius  and  some  of  the  cones  and  cra- 
ters of  the  Phlegrean  fields,  considered  in  reference  to  the  same  questions. 
Recent  Shower  of  Ashes  of  Sept,  from  Etna. — On  my  way  to  Catania  (October  1857), 
I was  showTi,  when  passing  through  Aci  Reale,  some  of  the  pulverized  scoriae  which  had 
been  showered  down  on  that  city  a few  weeks  before,  on  the  6th  of  September,  1857, 
from  the  summit  of  Etna,  no  less  than  fourteen  miles  distant.  I was  informed,  that  while 
this  dust  was  falling  on  the  roofs  of  the  houses  and  pavement  of  the  streets,  loud  deto- 
nations were  heard  at  Aci,  and  a whirling  column  of  dense  smoke  was  seen  to  rise  from 
the  crater.  The  shape  of  the  cone  at  the  same  time  underwent  a marked  change,  in 
consequence  of  which  it  now  deserves  even  more  than  formerly  its  ancient  epithet  of 
“bicornis.”  [When  I ascended  to  the  summit  of  Etna,  October  1858,  I found  that  this 
same  fall  of  sand  and  lapilli,  being  a hundredfold  more  voluminous  near  the  focus  of 
eruption,  had  levelled  up  the  superflcial  irregularities  of  the  lava  of  1838,  lying  at  the 
eastern  base  of  the  cone  to  such  an  extent  that  I could  cross  it  with  my  mule.  I also 
.saw  large  angular  fragments  of  a dark  dolerite,  3 or  4 feet  in  diameter,  thrown  out  at  the 
same  period  to  great  distances  from  the  crater,  and  resting  on  the  gently  inclined  slope 
S.E.  of  the  base  of  the  cone.  My  guides  assured  me  that  the  highest  part  of  the  rim  of 
the  crater  had  lost  much  in  height  during  these  explosions,] 
Allucial  deposits  and  external  features  of  the  coast  along  the  eastern  base  of  Etna. 
c8[MTien  travelling  by  the  coast  road  along  the  eastern  base  of  Etna,  the  geologist 
cannot  fail  to  be  struck  with  the  extent  and  thickness  of  an  alluvial  deposit,  from 
50  to  150  feet  thick,  which  skirts  the  shore  from  as  far  north  as  the  Fiume  Freddo  to 
as  far  south  as  Prajola,  a distance  of  about  ten  miles.  This  alluvium,  as  I afterwards 
learnt,  stretches  inland  for  three  or  four  miles,  forming  a terrace  or  platform  on  which 
several  towns,  such  as  Giarre,  are  situated.  It  contains  fragments  of  such  rocks  as  1 
of  from  100  to  300  feet,  have  flowed  down  on  each  side  of  the  ridge.  These  newer  lavas,  which  are  very 
similar  in  composition  to  the  older,  are  fragmentary,  like  those  of  Etna,  on  the  surface,  or  broken  up  into 
pieces  for  a depth  of  several  feet ; but  no  section  affords, an  opportunity  of  determining  whether  they  con- 
tain solid  beds  in  the  interior. 
Professor  Smtth  has  advocated  Von  Buch’s  theory  of  upheaval  in  reference  to  the  more  ancient  parts 
of  Teneriffe,  but  regards  the  central  or  modern  cone,  to  which  the  above-mentioned  inclined  beds  of  por- 
phyritic  obsidian  belong,  as  a cone  of  eruption.] 
