WHICH  HAVE  COJS^SOLIDATED  ON  STEEP  SLOPES. 
781 
America,  which  are  nearly  all,  if  not  all,  identical  with  mollusca  still  inhabiting  the 
northern  hemisphere.  Notwithstanding  which,  a large  part  of  the  European  area  has 
been  turned  from  sea  into  land,  or  from  land  into  sea,  since  the  commencement  of  that 
glacial  period,  while  the  present  distribution  of  living  species  of  plants  and  animals 
throughout  the  continents  and  islands  has  been  entirely  established  since  the  time  when 
the  transportation  of  erratic  blocks  by  ice  took  place. 
Recajpitulation  of  Part  III.,  and  concluding  remarks  on  “ Craters-of-elevation.” 
Having  recapitulated,  at  pages  737  and  761,  the  principal  conclusions  arrived  at  in 
the  first  and  second  parts  of  this  memoir,  I shall  now  give  a brief  summary  of  those 
which  I have  endeavoured  to  establish  in  this  third  part. 
1st.  Some  valleys  or  rarines  were  formed  by  aqueous  erosion  on  the  flanks  of  Etna 
before  the  existence  of  the  Val  del  Bove,  nevertheless  a large  proportion  of  the 
transported  materials  at  the  eastern  base  of  the  mountain  was  accumulated  during  the 
formation  of  that  valley,  which  was  in  part  due  to  aqueous  erosion. 
2ndly.  The  first  depressions  in  which  the  Val  del  Bove  originated  may  have  been  due 
to  the  sinking  in  of  the  ground,  and  also  to  lateral  and  paroxysmal  explosions  unaccom- 
panied by  the  emission  of  lava. 
3rdly.  A gradual  upward  movement  of  the  coast  has  carried  up  to  considerable  heights 
the  more  ancient  alluria]  fonnations  at  the  eastern  and  southern  base  of  Etna,  together 
with  the  subjacent  marine  tertiary  strata;  and  this  movement  continued  down  to  very 
modern  times,  and  perhaps  still  continues. 
4thly.  The  allurial  deposits  of  the  valley  of  the  Simeto  were  both  marine  and  fluvia- 
tile,  the  latter  containing  some  remains  of  extinct  terrestrial  animals,  but  the  whole 
probably  of  post-pliocene  date,  and  coeval  with  the  subaerial  portion  of  Etna. 
5thly.  All  the  shells  of  the  tertiary  strata  of  the  eastern  base  of  Etna,  which  are 
abundant,  belong,  with  one  or  two  exceptions,  to  species  now  living  in  the  Mediterra- 
nean, and  the  newer  pliocene  strata,  in  which  they  are  imbedded,  were  probably  coeval 
with  the  oldest  foundations  of  Etna. 
6thly.  In  certain  tuffs,  next  in  age  to  the  older  and  most  highly  elevated  alluvium, 
the  remains  of  terrestrial  plants  of  recent  species  occur. 
Lastly.  No  connexion  whatever  can  be  traced  between  the  general  movement  of 
upheaval  which  has  accompanied  the  growth  of  Etna,  and  the  conical  or  dome-like  form 
of  the  mountain ; and  even  where  local  eruptions  have  burst  through  the  tertiary  and 
alluvial  strata,  these  last  have  not  been  lifted  up  in  such  a manner  as  to  favour  the 
hypothesis  of  craters  of  elevation. 
Reverting  now,  in  conclusion,  to  the  phenomena  described  in  Part  I.,  by  which  the 
capabihty  of  lava  to  consolidate  on  steep  slopes,  and  to  form  thereon  continuous  and 
tabular  masses  of  crystalline  rock,  is  demonstrated,  I may  observe,  that  we  can  henceforth 
dispense  with  the  sudden  and  terminal  catastrophe  to  which  the  leading  dogma  of  a 
certain  school  of  geologists  would,  if  adopted,  force  us  to  resort,  in  order  to  account 
for  the  highly  inclined  beds  in  every  large  volcano.  The  chief  question  which  still 
