WHICH  HAVE  CONSOLIDATED  ON  STEEP  SLOPES. 
751 
This  aiTangement  of  the  beds,  first  observed  by  Baron  S.  voisr  Walteeshausen,  I 
verified,  as  before  stated  (p.  741),  in  1858,  in  the  projecting  promontories  of  rock  called 
Cuvigghiuni,  Serra  Intermedia,  and  Vavalaci  (see  Map).  In  one  of  these  (Cuvigghiuni) 
S.  VON  ^YALTEESHAUSEN  Counted  no  less  than  forty  dikes  of  various  ages,  which  have 
invaded  the  inclined  strata,  the  oldest  dikes,  composed  of  greenstone,  being  often  of 
great  width,  and  being  crossed  and  shifted  by  the  more  modern  or  doleritic  ones,  and 
many  of  both  kinds  being  out  of  the  perpendicular. 
Here  and  in  the  adjoining  Serra  Intermedia,  there  are  points  where  the  volume  of 
the  intrusive  matter  seems  equal  to  the  rocks  which  they  penetrate,  and  we  cannot  there- 
fore be  sm’prised  if,  under  such  circumstances,  we  should  see,  in  the  lower  half  of  the 
escarpment,  dips  exceeding  40°,  an  inchnation  which  we  cannot  ascribe  to  the  original 
position  of  the  beds.  But  after  measuring  the  dip  at  numerous  points,  even  here,  where 
the  dikes  most  abound,  I found  it  rarely  above  33°,  while  occasionally  it  only  amounted 
to  15°.  Amidst  all  these  variations  I saw  no  case  of  a reversed  dip,  or  a dip  towards 
the  Val  del  Bove.] 
The  beds  in  the  lower  half  of  the  Serra  del  Solfizio  were  probably  from  the  first  very 
steeply  inclined,  for  they  consist  chiefiy  of  agglomerates,  containing  many  angular  frag- 
ments of  lava,  implying  a neighbouiing  vent ; and  we  need  not  perhaps  attribute  more 
than  a fifth  part  of  their  present  dip  to  a tilting  of  the  mass  by  subsequent  dis- 
turbances. 
The  fact  that  the  steepest  dips  occur  where  the  dikes  are  most  numerous,  may  be 
thought  by  many  to  favour  the  doctrine  that  the  high  inclination  of  the  beds  was  the 
effect  of  the  injection  of  melted  matter  into  such  innumerable  fissures.  Without  deny- 
ing that  it  may  sometimes  have  been  an  auxiliary  cause,  we  must,  on  the  other  hand, 
remember  that  the  dikes  are  always  nearest  the  great  centres  of  eruption,  and  that 
there  are  three  reasons  why  the  original  dips  should  be  greatest  near  such  centres : — 1st, 
because  the  heavier  and  larger  fragments  of  rock  thrown  out  of  the  crater  fall  nearest  to 
its  margin;  2ndly,  because  the  red-hot  scoriae,  as  before  mentioned,  are  sometimes 
agglutinated  together;  and  3rdly  (an  infiuential  circumstance  too  often  overlooked),  be- 
cause streams  of  lava  frequently  stop  short  when  they  have  crept  but  a small  way  down 
the  declivity  of  the  cone.  [The  effect  in  steepening  its  fianks  of  this  midway  halting  of 
many  lavas,  was  strikingly  exemplified  high  up  on  the  north  slope  of  Vesuvius,  between 
the  years  1855  and  the  close  of  1857,  especially  in  July  of  the  year  last  mentioned.  The 
inclinations  of  the  recent  lavas  observed  by  Signor  Guiscaedi  and  me,  amounted  to  30° 
and  35°,  and  even  for  short  distances,  39°  and  42°.] 
\8upjposed  frequent  injection  of  lava  in  beds  conformable  to  tufaceous 
strata.,  considered. 
It  has  been  abeady  hinted  (p.  749)  that  S.  von  Walteeshausen  attributes  much  of  the 
upheaval  of  the  mass  of  Etna  to  the  intrusion  of  conformable  lavas  between  previously 
deposited  layers  of  tuff  and  fragmentary  matter.  He  ascribes,  for  example,  such  an 
MDCCCLVIII.  5 F 
